Two days ago I found some wallpapers are replaced to "Oops" image instead of original ones. To my understanding, it is made by a site to avoid their pictures from downloading without showing their advertisement banners. The site is included in my directory, from which a recommended pictures are selected by matching user keywords.
Basically I don't have any pictures becase of copy right reason, and the service has a directory of pictures with thumbnails, so that it acts as a kind of search engine of images. (Only exclusion is nasaimage, and we provide under its rule of copyright). And I think that it is fair for each sites to decide how to distribute their contents, so I should respect their desision and give up checking the site technically.
Then I remove the site URL from the directory and rebuild a database of picture pool. And I feel disappointed to find that the number of pictures in the pool is decreased to be a half of the day before.
I think to be a risk that my service depends much on a few other's site. So I add three small wallpaper sites in the directory Yesterday. It does not increase the number dramatically, but I'd like to add many other site to be the number of pictures up to 10 thousand again.