I don't think they need to have any meaning. And I think that even if initially you had no reason for getting a certain tattoo, you just get it because you like it; you may find that in 10 years time you look back and it has a lot of meaning and memories attached to it without it being intentional.
Admittedly, the only tattoo I have is meaningful to me, it reminds me of the joy and love that all my kittehs have brought to me throughout my life, and makes me smile =)
But there are other images that i really like that don't have any particular relevence to me personally, but i find them to be beautiful and pleasing images that would make my body feel beautiful and pleasing should i ever choose to get more tattoos.
It actually grinds my gears a bit when someone comes up with a deep and elaborate meaning for a really generic repeated image... i know it shouldn't but it does. I think some people feel obliged to have a reason for getting a tattoo when really it shouldn't matter.