Well, most animated graphics files on websites are either "GIF" or "Compuserve GIF" files. The "GIF" format (created/introduced by Compuserve), can contain multiple 'frames' each with a set of instructions as to how to display itself, how long to display itself, and what to do next.
Havent had a need to make to many animated graphics in some time, so its been awhile, I dont know the more current applications. But im going to check out this PhotoPlus and see if I can help out. Hoping the "PhotoPlus 6.03" I found is the same thing you have.
You mentioned animating two photos. Do you mean just changing back and forth between one and the other?
"How" will vary alot on the application used to create them.