Digital collage using PaintBook App on my iPod Touch of a previous Paintbook drawing, an acrylic painting on paper, and a digital photo.
Drawings were from life, imagination and photos.

PaintBook is definitely a contender with Juxtaposer for collaging as you can fully resize, rotate, and erase (to transparency) parts of each layer, and it has seemingly infinite numbers of layers which you can also show, hide, merge etc.

Juxtaposer’s interface for doing this is much better but Juxtaposer’s resolution is pathetic, while Paintbook’s is excellent. Of course it will depend on your source images, too, but you can save files up to 16 mg in size.

I bet those ladies on the bench are happy to be transported from the train station, where they started out…