If the tumblr site is going to remain active I would lean towards using the Tumblr API to get at the photos. You could then just write some javascript/jquery functions to display the images however you want.
I've done something similar in the past with Google Picasa Albums and it worked out pretty well.
http://www.tumblr.com/docs/en/api/v2#photo-posts
Just a little additional info, in the past I've found using jquery plugins sometimes makes it a bit mor simple to get at the data I'm looking for.
Never used this one in particular but just a quick search and found this as an example of one that might be helpful.
https://github.com/Iaaan/jQuery-plugin-for-Tumblr-API