The problem with the bald young Picard, it is an insult to the audience. It's saying "the audience isn't smart enough to figure this out unless we make the young Picard in the photo bald."
The impression I got was they wanted a picture of Tom Hardy as a younger Picard in the movie, to help sell the idea that Shinzon is Picard's clone. Since Hardy was shaving his head to be Shinzon, young Picard had to be bald by necessity. The only real alternative was to have Hardy wear a toupee, but that could have looked silly, so they went with the bald look.
Which there is nothing wrong with. It's easily explained that he had his head shaved for any variety of reasons, he lost a bet, hazing, charity. There are worse continuity errors in Star Trek, hell worse things in Nemesis to get hung up on.