I'll check this out, and let you know what I find.

Sorry for taking so long, but I've done a bit of digging around on this. It turns out that DisplayFusion was only looking in the most recent 100 images for a search. However, the Flickr API will only return a maximum of 500 images, so I've changed it to this value. It won't look at all the images in a search, only the newest 500. This isn't perfect, but it's better than 100 and the best I can do until Flickr raises the limit in their API.