Low Price Image Agency YayMicro.com Reaches 1 Million Royalty Free Images ...
Benzinga
The interest and use of social media channels, such as microstock forums and blog community, together with a user-friendly technology gave YAY a head start ...

PicScout Makes Image Credit Available to All for Free -- Spurs Industry-Wide ...
PR-USA.net (press release)
... by a tiered pricing structure for additional clicks based upon the image's licensing status: rights managed, royalty free and microstock images. ...

Dreamstime offers four extended licenses which could increase your earnings significantly: Increase Max Copies, Web Usage, Print Usage, and Sell the Rights. Each of these extends the ways in which the image can be used and pays a much higher premium. If you sell the rights to the image, you no longer control it and cannot sell it elsewhere, so use it with caution--noting that you can make a large chunk of change using this option (you can set your own price). Further details are below.