Valid formats are png, jpg and gif. It must not be blurry. '''Most times it's best to zoom in as much as possible to a representative area of the screen, not the whole screen of the app.''' They must be uploaded in the Amahi wiki and referenced in the app. Please do not reference images from other sites. If you need a quick image editor, you can use the free online image editor [http://aviary.com/apps/flash/aviary/index.aspx?tid=1&Phoenix Phoenix], by Aviary.