Image Comparer is a 照片 duplicate finder program for Windows. Works well with my Nikon RAW files. It compares visually, so it can detect resized 或者 rotated photos. I am using it to automatically 删除 照片 duplicates with lower resolution.
This is the 摄影 section in art neighbor.com which is a very intriguing site for artists and collectors to showcase their work and network with other artists/ collectors. I found this to be a valuable resource.