Having done this myself for large forums, I think we had a single DMCA. Bandwidth costs are relatively inexpensive, too. You can cache images for an indefinite

Having done this myself for large forums, I think we had a single DMCA. Bandwidth costs are relatively inexpensive, too. You can cache images for an indefinite amount of time, serving them over your existing CDN, and purge the older cache based on last-to-access. I've not been blocked from any image hosting sites.