I love creative baby pictures! I saw this idea on Pintrest (crocheted) and decided to give it a try.
I used a skirt I had that had nice pretty ruffles on the bottom (makes a nice fin part & the top part). The measurements I used is 7.5" wide and 20" long (not including the fin part). One note: This fit my newborn (2 weeks/8 lb.) great... but if you are making for a bigger baby I would make it wider... I also make a pretty flower/pearl headband to go with it.
To see my tutorial on how I took these pictures myself (non professionally) go here.