Well I'd imagine even if there's some sort of galaxy spanning internet, it wouldn't be hard to see why Tatooine might not have it. Also, I don't think it's so hard to believe the Empire would be able to completely suppress info about the jedi.

More generally I don't think I believe there is a galaxy spanning internet. Star Wars is more of a fantasy than a sic-fi story, so I like to see it in fantasy terms. I'm sure there are books and such around about the jedi, and people tell tales of course, but I'm not surprised that in his years on the run, Luke was not able to attain a photograph of Yoda. As well, I doubt Tatooine is a place of much culture, so I doubt too that Luke would have heard about Anakin from anyone but Owen.