The four iOS apps used to modify the photos of my Boston Jasper below are from left to right: Steampunk PhotoTada!, HOPE Poster!, Popstamatic, and Phototropedelic.
These are fun filters for artifying your photos. Out of all of them, Popstamatic has the least going for it, which is fortunate because it is the only free one. It “Warholizes” your photo, but unfortunately the palette is limited to mostly greens, and no reds and purples. The output is also the smallest. When using a 2000×2000 pixel image, it outputs it to only 600×600.
HOPE Poster! is best at doing what the name implies: Obamafying your photo. It gives other color combinations you can use besides the classic red, off-white and blue, but mostly it just adds a tint to your photo rather than separates it into three colors like the Obama tri-color one. You can also play around with the controls to create a negative image. The output is a generous 1536×2048, or double the screen resolution of the iPad.
Steampunk PhotoTada! is quite a fun experience. The interface is beautiful, done up in the requisite antiquey cogs. There are various old-timey effects you can add to the photo itself, and a choice of lovely realistic frames. When using a large image as input, I used the 2000×2000 pixel image of Jasper, it outputs it at 1000×1000. Not bad. But when using the camera within the app, the output is only 480×640, plus there is white area around the photo. I would suggest importing photos from a higher resolution source for this one.
My favorite is Phototropedelic. It applies a 1960s Peter Max style cartoon effect to photos. You can run the same photo over and over until you get just the right effect. And it saves it out not only as PNG files, but PDF, so you can blow them up real good to create print-ready posters in any size.
You can view more images in my galleries below to get a feel of what can be created: