I have an idea that can improve the migration process a bit.
Considering imgur trackthat Imgur tracks when an image that they host is being viewed, or at least the amount of times it was viewed, my suggestion is simple: do not migrate images that were never viewed, or with only the one view of the uploader after it was uploaded.
Advantages:
- Saving resources. No need to store something that's not being in use.
- Even more important: privacy. Personally I've uploaded images then on second thought didn't use it, and I'm certain others uploaded sensitive things by mistake, and corrected it without ever actually posting the image URL, hence adding images that were never viewed.