All these are smartphone apps that are working for websites that provide stock photos. These photos are used by website owners, bloggers and other commercial entities. All you need to do is take photos and upload it on the app. It's so easy !!!!
Twenty20 - This is a very good app. Photos can be uploaded very fast. Lots of challenges are available in different themes. Prize ranges from 20$ to 60$ per challenge. For those who want to buy photos this is a special link which will give you 40$ off.
Snapwire- Snapwire also got challenges. You can upload photos and if the buyers like the photos you will be paid for it.
Stockimo- Stockimo is another one. This one has got a rating programe. The photos you upload will be rated on a scale of 4. Your photo needs a rating above 2 to be accepted. This app claims to pay highest for photos. Professional photographers can earn a lot from this. Once a photo is accepted it can be sold again and again!!!