Last fall I drew a pumpkin a day for the month of October. I used my iPad with the app Sketchbook Pro and drew them all with my finger. I have also down loaded their mobile app for my iPhone and have been experimenting with that. I went to a lecture by Dan Marcolina who has done a lot of work with photographs on the iPhone and with different apps to manipulate images. (He has a book on the subject, iPhone Obsessed: Photo editing experiments with Apps.)
Sooooo, I’ve been playing with my phone. In addition to Sketchpook pro which lets one add photos to layers to use with their drawing tools, I’ve downloaded Tiffen’s Photo fx which contains all sorts of filters, grain presets, etc, etc, etc! There are so many other apps but this is where I’ve begun.