To some this may seem like collecting in quarters and cents but what Photoglif is offering is 20% out of their earnings through adsense to sites that publish their ad supported images or the developers who use these images in widgets or in applications.
As for best practices, as long as the images are used as embed codes provided in the return from the API you are pretty much free to do what you wish. The development needs to comply with our standard TOS, but really what we are hoping is this project gives developers a very robust and rich set of always growing professional content to work with when building widgets, plugins, and mashups that need content.
If you wish you can contact Mike at fotoglif
Check out the website: www.fotoglif.com