If you want to create line drawings from photos then have a look at Inkwork. The image above was created from a photo of my ugly mug. The quality of the line work will depend on the original image, but generally it does a great job
I recently downloaded the KaleidaCam app (when it was free for a day) and have been having some fun trying it out. This is one of the many images I have produced. I used the Perspective Correction app to add perspective, then imported the picture into ArtStudio to create a new header image for the blog. KaleidaCam is a fantastic little app with a great range of options even without the upgrade but I upgraded it anyway as it was only $1.29 AUD and I had saved $1.99 AUD by getting the app itself for nothing. Just love these free apps. The first thing I do every morning is fire up AppAdvice and check out the latest free apps.