Image Screening of Graffiti

I’m interested in image screening and thinking to use that technique in my thesis, so I would like to use to use this opportunity to learn the skill.
A webpage for the sample study: http://gizmodo.com/this-nifty-tool-turns-google-street-view-into-a-graffit-1595919773

I will pretty much replicate what Sarah Zhang has done and learn how image screening works. I haven’t decided the area of study, but if the data is available, I would like to track the changes in somewhere NYC.