Valid formats are png (much recommended), jpg and gif. The best logos are well centered with the logo covering most of the image and transparent background. 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.