As pointed out in another post , there are some issues with the loading times. But even when it's fast, we have to wait some seconds from one image to another. It seems minor, but that's a lot if you mark many images .
Would it be very difficult or troublesome to add the possibility of downloading the next image just after loading the current one? That way, while you are marking your image, the next is being "prepared" in the background, shortening the waiting time dramatically.
Another way to fix this problem is to add offline capabilities. This was mentioned by starstryder, but she was referring to a mobile app. I don't know whether that would cause more problems related to the number of users reviewing each image, etc.
What's your opinion on this issue?