I know there's a computer program of some kind for merging two pictures, which I guess would be done successively to get varying amounts of boy or lizard.

But if no one knows what the program is I guess I'm stuck anyway. Thanks for your time.

I agree with Demonte, those were each drawn.
The closest thing I could think to do is using photoshop to combine two creatures or whatever, but it isn't "morphing" as you seem to want it.

I guess you would have to draw it. Those look like they were drawn. Maybe there is an effect on Photoshop, Gimp, or whatever you use, but I use both and don't know of any effects. Sorry if it's not what you were looking for, but drawing is the only answer I can think of. Try looking for tutorials for the program you use. That might help.