I posted a photo of an american traditional tattoo to my instagram page. It's not my tattoo, but a tattoo done by one of my favorite artists.

Someone commented "Word," on the post. I know usually that's slang to agree with something, but that makes no sense in this context. Can anyone understand?

You're right, it really does make no sense. Honestly, it makes no sense to me in any context but I get it. So that is probably what the person who wrote it meant... and they were just trying to be "cool" about it. They were probably saying they liked it.

If 'word' is slang for agree, maybe it's also a new variation on 'like.' Clicking LIKE on Facebook all day really wears that out.