My sister lives in Katy, so I get out that way some, but I'm not all that acquainted with the Katy area outside of their particular neighborhood. But here are a couple of ideas anyway. At the Pin Oak exit from the Katy Fwy (I-10), if you head north, you'll come to "Old-Town" Katy. When you get to the train tracks and the grain silos, real close to there is a caboose that's been put on display with its own little pocket park. It's a photogenic area if you like using the caboose as a backdrop.
You can also get to the Katy Mills Mall from the Pin Oak exit and the next one east. The Katy Mills Mall is very big, and you might find a number of interesting photo backdrops there. Those are the only two places I can think of offhand.