We have features a few nice photo apps that can add various effects to your photos, but if you want to turn your photo into sketch, the photo app My Sketch may be more suitable for you.
My Sketch is an interesting photo app developed by Wilson Tjoa, and designed for both iPhone and iPad. The universal app features intuitive and clear layout, and comes with 20 different types of sketches in order that you can easily turn your photos into extraordinary sketches, while the adjustment of brightness and contrast allows you to further modify your sketches. You can directly take photo in the app, or import photo from photo library. Apart from that, after finishing the conversion, you can also share your sketches with friends via Facebook, Twitter, Tumblr, Flickr and Email.
My Sketch with size of 18.8 MB is compatible with iPhone, iPod touch and iPad running iOS 4.0 or later. At present, the universal app is free for a limited time. If you’re interested, jump to App Store for more details.