Issue/451 data attribute instead of

Solves #451 by using a data attribute instead of id to identify images.
I think that for the purpose of this PR I'd just implement a method to get the ID, and another to get the element, but with the same code you already have.  The reason for this is that I'd avoid adding more features in right now.

If you think it'd be a good idea to also make the change you're suggesting I'd consider opening a different ticket.

That way we can just make sure this is pushed fast today, and make improvements afterwards.