I'm having this problem currently. Safebooru is saying I'm not providing a valid image/image is corrupted or already on the site. I can't find the image here yet, and I've tried multiple URLs. Not sure what's going on...
...So, I'm still having his problem from time to time. I tried uploading directly from Gelbooru, too, but: -"An error occured. The image could not be added because it already exists or it is corrupted." ?????????