Ticker supplied image doesn't work

[idrostasi]

If I go into the tab "Menu/Plugins option" then in the subtap "Plugins option", under RSS Image Selection I can choose Ticker supplied image.
But even if I select the image into InfoService plugin of MediaPortal, I don't get any image into the RSS feed skin.
Maybe format and resolution of the image I chose are bad? Which is the right procedure to get the image into the skin for the RSS feed?