PicSketch is a US$1.99 universal app that takes any photo on your iOS device and turns it into an image that looks like it was sketched. Using the app is a two-click operation. One click lets you select the style of sketch; another click lets you select a color or mono background.
You can explore several of the options, and when satisfied either save the photo or share it. The app gives you 22 pencil sketch styles, five sketch effects like B&W and color and 18 different retro-looking sketch backgrounds.
The app works as advertised, but I never felt the photo itself had the true look of a sketch. Instead, it looks like a photograph that's surrounded by brush strokes. Meanwhile, significantly more expensive applications like Photoshop and third-party plug-ins can achieve the effect more successfully. PicSketch produces nice results without looking like a true sketch.