diff --git a/README.md b/README.md
index ae14895..43b9f1d 100644
--- a/README.md
+++ b/README.md
@@ -83,6 +83,21 @@ If you just want to receive photo data for the most recent Sol for which photos
 
 https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/latest_photos?api_key=DEMO_KEY
 
+#### Size parameter:
+
+Specify the size of the photo you would like to receive. Default value is `large`.
+
+https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/photos?api_key=DEMO_KEY&size=small
+
+| Size Parameter Value | Format | Curiosity   | Opportunity | Spirit | Perseverance |
+|----------------------|--------|:-----------:|:-----------:|:------:|:------------:|
+| `small`              | JPEG   | ✔           | ✔           | ✔      | ✔            |
+| `medium`             | JPEG   | ✔           | ✔           | ✔      | ✔            |
+| `large`              | JPEG   | ✔           | ✔           | ✔      | ✔            |
+| `full`               | PNG    | N/A         | N/A         | N/A    | ✔            |
+
+*Note: Only **Perseverance** `small`, `medium`, and `large` size images have guaranteed widths of `300px`, `800px`, and `1200px` respectively. All other dimensions are variable.*
+
 ### Mission Manifest Endpoint
 
 A mission manifest is available for each Rover at the `/manifests/<rover_name>`. This manifest will list details of the Rover's mission to help narrow down photo queries to the API. The information in the manifest includes:
diff --git a/app/controllers/api/v1/latest_photos_controller.rb b/app/controllers/api/v1/latest_photos_controller.rb
index 81048bd..abea7a7 100644
--- a/app/controllers/api/v1/latest_photos_controller.rb
+++ b/app/controllers/api/v1/latest_photos_controller.rb
@@ -1,26 +1,21 @@
 class Api::V1::LatestPhotosController < ApplicationController
   def index
-    def index
-      @rover = Rover.find_by name: params[:rover_id].titleize
-      if @rover
-        render json: search_photos, each_serializer: PhotoSerializer, root: :latest_photos
-      else
-        render json: { errors: "Invalid Rover Name" }, status: :bad_request
-      end
-    end
-  end
+    rover = Rover.find_by name: params[:rover_id].titleize
 
-  private
+    if rover
+      validated_params = params
+        .permit(:rover_id, :camera, :earth_date, :size, :page, :per_page)
+        .merge(sol: rover.photos.maximum(:sol))
+      photos = helpers.search_photos rover, validated_params
 
-  def photo_params
-    params.permit(:camera, :earth_date, :rover_id).merge(sol: @rover.photos.maximum(:sol))
-  end
-
-  def search_photos
-    photos = @rover.photos.order(:camera_id, :id).search photo_params, @rover
-    if params[:page]
-      photos = photos.page(params[:page]).per params[:per_page]
+      begin
+        photos = helpers.resize_photos photos, validated_params
+        render json: photos, each_serializer: PhotoSerializer, root: :latest_photos
+      rescue PhotoHelper::InvalidSizeParameter => e
+        render json: { errors: e.message }, status: :bad_request
+      end
+    else
+      render json: { errors: "Invalid Rover Name" }, status: :bad_request
     end
-    photos
   end
 end
diff --git a/app/controllers/api/v1/photos_controller.rb b/app/controllers/api/v1/photos_controller.rb
index fac711c..9963c86 100644
--- a/app/controllers/api/v1/photos_controller.rb
+++ b/app/controllers/api/v1/photos_controller.rb
@@ -1,13 +1,29 @@
 class Api::V1::PhotosController < ApplicationController
+  before_action :photo_params
+
   def show
-    photo = Photo.find params[:id]
-    render json: photo, serializer: PhotoSerializer, root: :photo
+    photo = Photo.find @params[:id]
+
+    begin
+      resized_photo = helpers.resize_photo photo, @params
+      render json: resized_photo, serializer: PhotoSerializer, root: :photo
+    rescue StandardError => e
+      render json: { errors: e.message }, status: :bad_request
+    end
   end
 
   def index
-    rover = Rover.find_by name: params[:rover_id].titleize
+    rover = Rover.find_by name: @params[:rover_id].titleize
+
     if rover
-      render json: photos(rover), each_serializer: PhotoSerializer, root: :photos
+      photos = helpers.search_photos rover, @params
+      
+      begin
+        photos = helpers.resize_photos photos, @params
+        render json: photos, each_serializer: PhotoSerializer, root: :photos
+      rescue PhotoHelper::InvalidSizeParameter => e
+        render json: { errors: e.message }, status: :bad_request
+      end
     else
       render json: { errors: "Invalid Rover Name" }, status: :bad_request
     end
@@ -16,14 +32,6 @@ def index
   private
 
   def photo_params
-    params.permit :sol, :camera, :earth_date, :rover_id
-  end
-
-  def photos(rover)
-    photos = rover.photos.order(:camera_id, :id).search photo_params, rover
-    if params[:page]
-      photos = photos.page(params[:page]).per params[:per_page]
-    end
-    photos
+    @params = params.permit :id, :rover_id, :sol, :camera, :earth_date, :size, :page, :per_page
   end
 end
diff --git a/app/helpers/photo_helper.rb b/app/helpers/photo_helper.rb
new file mode 100644
index 0000000..dbfdc8b
--- /dev/null
+++ b/app/helpers/photo_helper.rb
@@ -0,0 +1,108 @@
+module PhotoHelper
+
+  def search_photos rover, params
+    photos = rover.photos.order(:camera_id, :id).search params, rover
+
+    if params[:page]
+      photos = photos.page(params[:page]).per params[:per_page]
+    end
+
+    photos
+  end
+
+  class InvalidSizeParameter < StandardError
+    def initialize(
+        size,
+        rover_name,
+        exception_type="custom"
+      )
+      super("Invalid size parameter '#{size}' for #{rover_name.titleize}")
+    end
+  end
+
+  def resize_photo photo, params
+    rover_name = photo.rover.name.downcase
+    suffix_data = lookup_suffix rover_name, params[:size]
+
+    if !suffix_data.nil?
+      replace_photo_suffix photo, suffix_data[:old_length], suffix_data[:new]
+    else
+      raise InvalidSizeParameter.new params[:size], rover_name
+    end
+  end
+
+  def resize_photos photos, params
+    rover_name = params[:rover_id].downcase
+    suffix_data = lookup_suffix rover_name, params[:size]
+
+    if suffix_data.present?
+      replace_each_photo_suffix photos, suffix_data[:old_length], suffix_data[:new]
+    else
+      raise InvalidSizeParameter.new params[:size], rover_name
+    end
+  end
+
+  private
+
+  def replace_each_photo_suffix photos, old_suffix_length, new_suffix
+    photos.map do |photo|
+      replace_photo_suffix photo, old_suffix_length, new_suffix
+    end
+  end
+
+  def replace_photo_suffix photo, old_suffix_length, new_suffix
+    new_photo = photo.clone;
+    new_photo.img_src = photo.img_src[0, photo.img_src.length - old_suffix_length] + new_suffix
+    new_photo
+  end
+
+  def lookup_suffix rover_name, size
+    suffix_hash = {
+      :curiosity => {
+        :original_length => 4, # .jpg or .JPG
+        :sizes => {
+          :small => '-thm.jpg',
+          :medium => '-br.jpg',
+          :large => '.JPG'
+        }
+      },
+      :spirit => {
+        :original_length => 7, # -BR.JPG
+        :sizes => {
+          :small => '-THM.JPG',
+          :medium => '-BR.JPG',
+          :large => '.JPG'
+        }
+      },
+      :opportunity => {
+        :original_length => 7, # -BR.JPG
+        :sizes => {
+          :small => '-THM.JPG',
+          :medium => '-BR.JPG',
+          :large => '.JPG'
+        }
+      },
+      :perseverance => {
+        :original_length => 9, # _1200.jpg
+        :sizes => {
+          :small => '_320.jpg',
+          :medium => '_800.jpg',
+          :large => '_1200.jpg',
+          :full => '.png'
+        }
+      }
+    }
+
+    rover = rover_name.downcase.to_sym
+    size = size.nil? ? :large : size.to_sym
+
+    if suffix_hash.key?(rover) && suffix_hash[rover][:sizes].key?(size) then
+      {
+        :old_length => suffix_hash[rover][:original_length],
+        :new => suffix_hash[rover][:sizes][size]
+      }
+    else
+      nil
+    end
+  end
+end
diff --git a/app/models/photo.rb b/app/models/photo.rb
index dbfd173..d112aa5 100644
--- a/app/models/photo.rb
+++ b/app/models/photo.rb
@@ -11,10 +11,8 @@ class Photo < ActiveRecord::Base
 
   def self.search(params, rover)
     photos = search_by_date params
-    if params[:camera]
-      if photos.any?
-        photos = photos.search_by_camera params, rover
-      end
+    if params[:camera] and photos.any?
+      photos = photos.search_by_camera params, rover
     end
     photos
   end
diff --git a/spec/controllers/api/v1/latest_photos_controller_spec.rb b/spec/controllers/api/v1/latest_photos_controller_spec.rb
new file mode 100644
index 0000000..a976013
--- /dev/null
+++ b/spec/controllers/api/v1/latest_photos_controller_spec.rb
@@ -0,0 +1,145 @@
+require 'rails_helper'
+
+describe Api::V1::LatestPhotosController do
+  let(:rover) { create(:rover) }
+  let(:camera) { create(:camera, rover: rover) }
+  let!(:photo) { create(:photo, rover: rover, camera: camera) }
+
+  suffix_hash = {
+    'Curiosity' => {
+      'small' => '-thm.jpg',
+      'medium' => '-br.jpg',
+      'large' => '.JPG'
+    },
+    'Spirit' => {
+      'small' => '-THM.JPG',
+      'medium' => '-BR.JPG',
+      'large' => '.JPG'
+    },
+    'Opportunity' => {
+      'small' => '-THM.JPG',
+      'medium' => '-BR.JPG',
+      'large' => '.JPG'
+    },
+    'Perseverance' => {
+      'small' => '_320.jpg',
+      'medium' => '_800.jpg',
+      'large' => '_1200.jpg',
+      'full' => '.png'
+    }
+  }
+
+  describe "GET 'index'" do
+    let!(:latest_photo) { create(:photo, rover: rover, camera: camera) }
+    before(:each) do
+      latest_photo.update(sol: 999)
+    end
+
+    context "with rover_id" do
+      before(:each) do
+        get :index, params: { rover_id: rover.name.downcase }
+      end
+
+      it "returns http 200 success" do
+        expect(response.status).to eq 200
+      end
+
+      it "renders photo data from most recent sol" do
+        expect(json["latest_photos"].first["sol"]).to eq 999
+      end
+    end
+
+    context "with bad Rover name" do
+      before(:each) do
+        get :index, params: { rover_id: "this doesn't exist"}
+      end
+
+      it "returns http 400 bad request" do
+        expect(response.status).to eq 400
+      end
+
+      it "returns an error message" do
+        expect(json["errors"]).to eq "Invalid Rover Name"
+      end
+    end
+
+    context "with camera query" do
+      before(:each) do
+        create_list(:photo, 3, rover: rover, camera: create(:camera, {name: 'TEST', rover: rover}), sol: 9999)
+        get :index, params: { rover_id: rover.name, camera: 'TEST' }
+      end
+
+      it "returns http 200 success" do
+        expect(response.status).to eq 200
+      end
+
+      it "renders photo data matching sol and camera" do
+        expect(json["latest_photos"].length).to eq 3
+        expect(json["latest_photos"].first["camera"]["name"]).to eq 'TEST'
+      end
+    end
+
+    context "with pagination" do
+      let(:params) { {rover_id: rover.name.downcase} }
+
+      before(:each) do
+        create_list(:photo, 35, rover: rover, camera: camera, sol: 9999)
+      end
+
+      it "returns 25 entries per page when a page param is provided" do
+        get :index, params: params.merge(page: 1)
+
+        expect(json["latest_photos"].length).to eq 25
+      end
+
+      it "returns all entries when no page param is provided" do
+        get :index, params: params
+
+        expect(json["latest_photos"].length).to eq 35
+      end
+
+      it "returns n entries per page when a per_page param is provided" do
+        get :index, params: params.merge(page: 1, per_page: 30)
+
+        expect(json["latest_photos"].length).to eq 30
+      end
+
+      it "returns the remaining entries on the last page of results" do
+        get :index, params: params.merge(page: 2, per_page: 30)
+
+        expect(json["latest_photos"].length).to eq 5
+      end
+    end
+
+    suffix_hash.each do |rover_id, sizes|
+      context "with rover_id '#{rover_id}'" do
+        before(:each) do
+          rover.update(name: rover_id)
+        end
+
+        sizes.each do |size, suffix|
+          context "and size '#{size}'" do
+            before(:each) do
+              get :index, params: { rover_id: rover_id, size: size }
+            end
+
+            it "modifies img_src" do
+              photo = json['latest_photos'].first
+              expect(photo['img_src']).to end_with suffix
+            end
+          end
+        end
+
+        context "with invalid size parameter" do
+          before(:each) do
+            get :index, params: { rover_id: rover_id, size: "not a size" }
+          end
+
+          it "returns http 400 bad request" do
+            expect(response.status).to eq 400
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/controllers/api/v1/photos_controller_spec.rb b/spec/controllers/api/v1/photos_controller_spec.rb
index bffae01..9d4f948 100644
--- a/spec/controllers/api/v1/photos_controller_spec.rb
+++ b/spec/controllers/api/v1/photos_controller_spec.rb
@@ -5,6 +5,30 @@
   let(:camera) { create(:camera, rover: rover) }
   let!(:photo) { create(:photo, rover: rover, camera: camera) }
 
+  suffix_hash = {
+    'Curiosity' => {
+      'small' => '-thm.jpg',
+      'medium' => '-br.jpg',
+      'large' => '.JPG'
+    },
+    'Spirit' => {
+      'small' => '-THM.JPG',
+      'medium' => '-BR.JPG',
+      'large' => '.JPG'
+    },
+    'Opportunity' => {
+      'small' => '-THM.JPG',
+      'medium' => '-BR.JPG',
+      'large' => '.JPG'
+    },
+    'Perseverance' => {
+      'small' => '_320.jpg',
+      'medium' => '_800.jpg',
+      'large' => '_1200.jpg',
+      'full' => '.png'
+    }
+  }
+
   describe "GET 'index'" do
     context "with no query parameters" do
       before(:each) do
@@ -121,6 +145,41 @@
         expect(json["photos"].length).to eq 5
       end
     end
+
+    suffix_hash.each do |rover_id, sizes|
+      context "with rover_id '#{rover_id}'" do
+        before(:each) do
+          rover.update(name: rover_id)
+        end
+
+        sizes.each do |size, suffix|
+          context "and size '#{size}'" do
+            before(:each) do
+              get :index, params: { rover_id: rover_id, sol: 829, size: size }
+            end
+
+            it "modifies img_src" do
+              photo = json['photos'].first
+              expect(photo['img_src']).to end_with suffix
+            end
+          end
+        end
+
+        context "with invalid size parameter" do
+          before(:each) do
+            get :index, params: { rover_id: rover_id, sol: 829, size: "not a size" }
+          end
+
+          it "returns http 400 bad request" do
+            expect(response.status).to eq 400
+          end
+
+          it "returns an error message" do
+            expect(json["errors"]).to eq "Invalid size parameter 'not a size' for #{rover_id}"
+          end
+        end
+      end
+    end
   end
 
   describe "GET 'show'" do
@@ -137,5 +196,36 @@
         expect(json["photo"])
       end
     end
+
+    suffix_hash.each do |rover_id, sizes|
+      context "one of #{rover_id}'s photos" do
+        before(:each) do
+          rover.update(name: rover_id)
+        end
+
+        sizes.each do |size, suffix|
+          context "with size parameter '#{size}'" do
+            before(:each) do
+              get :show, params: { id: photo.id, size: size }
+            end
+
+            it "modifies img_src" do
+              photo = json['photo']
+              expect(photo['img_src']).to end_with suffix
+            end
+          end
+        end
+
+        context "with invalid size parameter" do
+          before(:each) do
+            get :show, params: { id: photo.id, size: "not a size" }
+          end
+
+          it "returns http 400 bad request" do
+            expect(response.status).to eq 400
+          end
+        end
+      end
+    end
   end
 end
diff --git a/spec/factories.rb b/spec/factories.rb
index e55502e..4541fe9 100644
--- a/spec/factories.rb
+++ b/spec/factories.rb
@@ -14,7 +14,7 @@
   factory :photo do
     sequence :img_src do |n| "https://mars.jpl.nasa.gov/msl-raw-images/proj/" +
       "msl/redops/ods/surface/sol/00829/opgs/edr/fcam/FRB_471079934EDR_F044" +
-      "2062FHAZ00323M_.JPG#{n}"
+      "#{n}2062FHAZ00323M_.JPG"
     end
     sol { 829 }
     rover