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. There are dozens of inking styles to choose from. You can also adjust the line thickness and you can choose the colors for the ink and the background. 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.