The server admin can still access their own photos via the client. They wouldn't be able to access the photos of other users.

edit: To explain further why it's almost always desirable:

You guarantee that you and your users' information is safe if the server is compromised, if an admin goes rogue, or if local bodies of power request their information from you.

The information can't be sent to third-parties by design.

Any operations / transformations that need to be applied to the information will have to either be done via homomorphic encryption or on the client-side (which is much more likely to be open source / easy-to-deobfuscate compared to blackbox server code).