If you get used to posting your cool pictures to something like Instagram or Flickr, you can a lot about your pictures and your picture-based presence on social media.

Opensource app devs have gone wild before and there is a chance of repo hacking by a third party. 

You can't revert deletions. 

Yes, it's way less trust. But there is still a lot of trust. Especially for users that are just running the apps with default relay sets that can disappear at any moment. 
 

 In both of your examples media came from a camera or a phone so there’s likely a backup. 

Yes people with default relays will have to figure out how to get around that, but at least there are options. 

 How do you get around it?  

 Use more and different relays .. 

 Make it less than trivial for users to host their own relays. A no-brainer relay on every device you own and one or two in the cloud. 
Extra points: users' sovereign relays also serve themselves their clients, so there is no trust problem.  

 Make it less than trivial for users to host their own relays. A no-brainer relay on every device you own and one or two in the cloud. 
Extra points: users' sovereign relays also serve themselves their clients, so there is no trust problem.