This is a long overdue feature within Facebook, but now users are able to drag+drop photos within their photo albums in any order that they want. This is powered by Ajax. Dan Weatherford, a new Facebook engineer just one day said, “This is ridiculous, I’m just going to build this thing.”
You can completely reverse the order if you want as well. Below is a screen shot of one of my photo albums. You’ll notice at the top right that the third picture in the first row is being moved. The arrows that appear when moving the screen shot didn’t appear when I hit “Print Screen” to get the screen shot, but I’m sure you get the idea:
This announcement was made official by the Facebook blog.