feat: replace photo library detection with human face detection

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## Next
 
+- fix: remove photo library detection since it's not really possible ([#267](https://github.com/PostHog/posthog-ios/pull/267))
+- feat: add human face detection in images ([#267](https://github.com/PostHog/posthog-ios/pull/267))
+
 ## 3.15.9 - 2024-11-28
 
 - fix: skip capturing a snapshot during view controller transitions ([#265](https://github.com/PostHog/posthog-ios/pull/265))

PostHog.xcodeproj/project.pbxproj

@@ -128,6 +128,7 @@
 		DAC699EC2CCA73E5000D1D6B /* ForwardingPickerViewDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = DAC699EB2CCA73E5000D1D6B /* ForwardingPickerViewDelegate.swift */; };
 		DACF6D5D2CD2F5BC00F14133 /* PostHogAutocaptureIntegrationSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = DACF6D5C2CD2F5BC00F14133 /* PostHogAutocaptureIntegrationSpec.swift */; };
 		DAD5DD0C2CB6DEF30087387B /* PostHogMaskViewModifier.swift in Sources */ = {isa = PBXBuildFile; fileRef = DAD5DD072CB6DEE70087387B /* PostHogMaskViewModifier.swift */; };
+		DAF42BC72CFB13DC00BCEB60 /* CGImage+Util.swift in Sources */ = {isa = PBXBuildFile; fileRef = DAF42BC12CFB13D900BCEB60 /* CGImage+Util.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -401,6 +402,7 @@
 		DAC699EB2CCA73E5000D1D6B /* ForwardingPickerViewDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ForwardingPickerViewDelegate.swift; sourceTree = "<group>"; };
 		DACF6D5C2CD2F5BC00F14133 /* PostHogAutocaptureIntegrationSpec.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PostHogAutocaptureIntegrationSpec.swift; sourceTree = "<group>"; };
 		DAD5DD072CB6DEE70087387B /* PostHogMaskViewModifier.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PostHogMaskViewModifier.swift; sourceTree = "<group>"; };
+		DAF42BC12CFB13D900BCEB60 /* CGImage+Util.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "CGImage+Util.swift"; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -725,6 +727,7 @@
 		69EE82B82BA9C4DA00EB9542 /* Replay */ = {
 			isa = PBXGroup;
 			children = (
+				DAF42BC12CFB13D900BCEB60 /* CGImage+Util.swift */,
 				69B7F6062CF7702D00A48BCC /* UIImage+Util.swift */,
 				69EE82B92BA9C50400EB9542 /* PostHogReplayIntegration.swift */,
 				69EE82BB2BA9C53000EB9542 /* PostHogSessionReplayConfig.swift */,
@@ -1195,6 +1198,7 @@
 				69261D1D2AD967CD00232EC7 /* PostHogFileBackedQueue.swift in Sources */,
 				3AE3FB432992985A00AFFC18 /* Reachability.swift in Sources */,
 				69F518122BAC783300F52C14 /* CGColor+Util.swift in Sources */,
+				DAF42BC72CFB13DC00BCEB60 /* CGImage+Util.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

PostHog/Replay/CGImage+Util.swift

@@ -0,0 +1,34 @@
+//
+//  CGImage+Util.swift
+//  PostHog
+//
+//  Created by Yiannis Josephides on 30/11/2024.
+//
+
+#if os(iOS)
+    import UIKit
+
+    extension CGImage {
+        // This class can maintain many state variables that can impact performance. So for best performance, reuse CIDetector instances instead of creating new ones.
+        static var humanFaceDetector: CIDetector = {
+            let options = [CIDetectorAccuracy: CIDetectorAccuracyLow]
+            return CIDetector(ofType: CIDetectorTypeFace, context: nil, options: options)!
+        }()
+
+        private static var ph_human_face_detected_key: UInt8 = 0
+        var ph_human_face_detected: Bool? {
+            get {
+                objc_getAssociatedObject(self, &CGImage.ph_human_face_detected_key) as? Bool
+            }
+
+            set {
+                objc_setAssociatedObject(
+                    self,
+                    &CGImage.ph_human_face_detected_key,
+                    newValue as Bool?,
+                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC
+                )
+            }
+        }
+    }
+#endif

PostHog/Replay/PostHogReplayIntegration.swift

@@ -406,22 +406,41 @@
             image.imageAsset?.value(forKey: "_containingBundle") != nil
         }
 
-        // Photo library images have a UUID identifier as _assetName (e.g 64EF5A48-2E96-4AB2-A79B-AAB7E9116E3D)
-        // SF symbol and bundle images have the actual symbol name as _assetName (e.g chevron.backward)
-        private func isPhotoLibraryImage(_ image: UIImage) -> Bool {
-            guard config.sessionReplayConfig.maskPhotoLibraryImages else {
-                return false
+        private func isAnimatedImageView(_ view: UIImageView) -> Bool {
+            !(view.animationImages?.isEmpty ?? true)
+        }
+
+        private func containsHumanFaces(caLayer layer: CALayer) -> Bool {
+            if let content = layer.contents, CFGetTypeID(content as CFTypeRef) == CGImage.typeID {
+                // force-casting is safe here because of CFTypeID check above
+                return containsHumanFaces(cgImage: content as! CGImage)
             }
+            return false
+        }
 
-            guard let assetName = image.imageAsset?.value(forKey: "_assetName") as? String else {
-                return false
+        private func containsHumanFaces(image: UIImage) -> Bool {
+            guard let cgImage = image.cgImage else { return false }
+            return containsHumanFaces(cgImage: cgImage)
+        }
+
+        private func containsHumanFaces(cgImage: CGImage) -> Bool {
+            let detectAndCache: () -> Bool = {
+                var faceDetected = false
+                let ciImage = CIImage(cgImage: cgImage)
+                faceDetected = !CGImage.humanFaceDetector.features(in: ciImage).isEmpty
+                cgImage.ph_human_face_detected = faceDetected
+                return faceDetected
             }
 
-            if assetName.isEmpty { return false }
-            if image.isSymbolImage { return false }
-            if isAssetsImage(image) { return false }
+            return cgImage.ph_human_face_detected ?? detectAndCache()
+        }
 
-            return true
+        private func isSystemImageView(_ view: UIImageView) -> Bool {
+            // Came across some system image views like <_UICutoutShadowView> that were masked
+            // with maskAllImages options (e.g in this case this was a blurred background view of a UIPickerView)
+            // Let’s be prudent and add a general check on internal classes starting with _UI.
+            // We may need to be more explicit in the future
+            String(describing: view).starts(with: "<_UI")
         }
 
         private func isAnyInputSensitive(_ view: UIView) -> Bool {
@@ -467,9 +486,17 @@
         }
 
         private func isSwiftUIImageSensitive(_ view: UIView) -> Bool {
-            // No way of checking if this is an asset image or not
-            // No way of checking if there's actual content in the image or not
-            config.sessionReplayConfig.maskAllImages || view.isNoCapture()
+            // sensitive, regardless
+            if view.isNoCapture() {
+                return true
+            }
+
+            // detect human faces
+            if config.sessionReplayConfig.maskImagesWithHumanFaces, containsHumanFaces(caLayer: view.layer) {
+                return true
+            }
+
+            return config.sessionReplayConfig.maskAllImages
         }
 
         private func isImageViewSensitive(_ view: UIImageView) -> Bool {
@@ -481,13 +508,32 @@
                 return true
             }
 
-            if config.sessionReplayConfig.maskAllImages {
-                // asset images are probably not sensitive
-                return !isAssetsImage(image)
+            // system images are likely not sensitive
+            if isSystemImageView(view) {
+                return false
+            }
+
+            // symbol images are probably not sensitive
+            if image.isSymbolImage {
+                return false
+            }
+
+            // an animated image view (e.g spinner view) is most likely not a sensitive asset
+            if isAnimatedImageView(view) {
+                return false
             }
 
-            // try to detect user photo images
-            return isPhotoLibraryImage(image)
+            // detect human faces
+            if config.sessionReplayConfig.maskImagesWithHumanFaces, containsHumanFaces(image: image) {
+                return true
+            }
+
+            // asset images are probably not sensitive (unless they contain a face)
+            if isAssetsImage(image) {
+                return false
+            }
+
+            return config.sessionReplayConfig.maskAllImages
         }
 
         private func toWireframe(_ view: UIView) -> RRWireframe? {
@@ -662,7 +708,6 @@
     private protocol AnyObjectUIHostingViewController: AnyObject {}
 
     extension UIHostingController: AnyObjectUIHostingViewController {}
-
 #endif
 
 // swiftlint:enable cyclomatic_complexity

PostHog/Replay/PostHogSessionReplayConfig.swift

@@ -24,10 +24,10 @@
         /// Default: true
         @objc public var maskAllSandboxedViews: Bool = true
 
-        /// Enable masking of images that likely originated from user's photo library
-        /// Experimental support (UIKit only)
+        /// Enable masking of images that may contain human faces
+        /// Experimental support
         /// Default: true
-        @objc public var maskPhotoLibraryImages: Bool = true
+        @objc public var maskImagesWithHumanFaces: Bool = true
 
         /// Enable capturing network telemetry
         /// Experimental support