Screenshot from the Preferences/Appearance section of the web interface (I believe this option is also available in many of the Mastodon apps but I don't know the interface) "Sensitive content Media display (choose one of these three options) - Hide media marked as sensitive - Always show media - Always hide media - Show colorful gradients for hidden media (Gradients are based on the colors of the hidden visuals but obfuscate any details) - Always expand posts marked with content warnings"