(note- I use a Mac, so the process will be a little different under Linux or Windoze)
For the GIF's I have been doing lately, I start with several similar images, hopefully with interesting color variations.

Then I grab a medium sized image of each flavor, crop them so that they are identical sized, and use Graphic Converter to make the JPG's into GIF's.  If you mean business, it has a CONVERT feature that will do directories at a time.  Once I have the GIF's of each color I use GIFfun which is freeware I found at Versiontracker Then pick the timing in the preferences panel and it's drop and drag!

Gif Animation by morST

Gif Page 1- Phish Posters

Gif Page 2- Dylan Posters

Gif Page 3- The Assortment

Gif Page 4- Trey Posters