I'd say RIU is safer than say, youtube or facebook. If the authorities want to build a case against you, pics you posted on RIU isn't going to help them much. I could post a picture of anything, doesn't mine I did it or I have it. I'd be more worried about using my pone to phost/browse. If you come into contact with auth, they could will check your phone on the spot. Pictures on there and you might have a problem. What if you lose it or it gets stolen?
Also, even if you don't post pics, be cautious. More than one person has been ratted on by a computer tech when they had their computers worked on. Esp. if you drop it off somewhere and leave it. Or it gets stolen. Chances are you plants will be gone too, then.
This (and much more) has all been covered many times, but I guess it never hurts to keep safety in the forefront.
tldr; Yes, it's safe unless you fuck it up with too much information.