FlickrCash uses the Flickr API to search by CC license, build lightboxes, and keep a record of licensed photos you intend to use.
Augustine Fou, creator of FlickrCash, tells us:
I created FlickrCash because I found many really beautiful photos on Flickr but could not use them for “commercial” purposes like design work for clients, because there was no way to document I had a license to use it. FlickrCash is BOTH a search/find interface to more quickly find images on Flickr, and also a way to document that you have a license to use a specific image.
Sample of image search (currently only searches Flickr repository):
Sample of archived license, available for inspection at any time:
With this publicly archived license the image buyer can definitively prove they have the right to use a specific image for a specific purpose — so they can use it for client design work. Both image owner and image buyer are named signatories to the agreement, and an official date/time stamp is obtained from the NIST Atomic Clock to document the exact time the license was executed.