i guess there is pixelfed. but i would compare it more to instagram. many lemmy instances allow uploading pictures directly, so you dont necessarily need a separate host.

but where i see the biggest caveat, is costs. cloud storage is not cheap and pictures are extremely large compared to text. therefore some lemmy instances only keep uploaded pics for a certain amount of time.

I dont know whether imgur is keeping pictures for ever or not… so i am not sure if it federated imgur would solve the ‘amnesia issue’ of some lemmy instances.