There is a successor of Cropland Capture, Picture Pile, from the people behind Geo-Wiki. Like Cropland Capture, this tool / game uses a citizen science approach, in this case to track deforestation.
The game presents a series of side-by-side images of the same location several years apart and ask you the question whether “ you see tree loss over time?”. Options are yes, no or maybe.
Perhaps a bit to my surprise, this is fairly addictive and I love the idea behind it. And you can play it on your computer, tablet or phone. If you want to give it a try, go to http://www.geo-wiki.org/games/picturepile/ .