I’ve been working on and think about this issue for a bit too. So far what I’ve got is:
To help prevent copyright infringement/ help protect yourself in case it inevitably happens you can require the user to check off an acknowledgement saying something like “By clicking this acknowledgement I verify that I own the image I am uploading or have written consent and to upload it to this site”. Additionally, it should be written in your terms of service that you don’t own user uploaded images and users should not upload images to the site that they do not own or have permission to use. Also to help staff notice infringing images quicker make sure you provide a clear way for users of the site to report the images of others.
Another option, if you’d like to monitor the uploaded images even closer, is to have all user uploaded images have to be accepted by a staff member before they show up on the site.