system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't you get prosecuted for posting videos/picture of yourself doing drugs while you can for posting a murder you've committed?

I know murder is far worse than smoking a joint but I've always wondered what stops law enforcement, for example, from prosecuting people showing their illegal grows and smoking on camera.
gpt
Typically the picture is a starting point for an investigation. 

If you post a picture of you doing drugs, they interview you and you say "fifth amendment" or "it wasn't drugs. It was something that looks like but isn't drugs," that's where the investigation ends. 

If you post a picture/video of you killing someone, they open an investigation and comb the scene for evidence corroborating what you've said, look for a body, etc.