I just wrote up some docs on how to hide images in public rooms on Matrix in several clients.
If anyone was able to add info for more clients that would be awesome. Here's my change for reference: 
Public Rooms
Matrix is often use for public online discussions. Being an interoperable
protocol, it allows people using different providers to talk together onl...
GitHub
Document how to hide images in Element by andybalaam · Pull Request #2971 · matrix-org/matrix.org
As discussed within the Trust and Safety Research and Documentation Working Group.
✔️ Checklist
Check for common mistakes:
Wrap plain URLs...