Not just Texas. I recently bought a used copy of Sally Mann's Hold Still: A Memoir with Photographs. It had two stamps on it. One on the bottom edge that read "Chicago Public Library." The other on the top edge read "Discard." A bit strange for a good book that was just published in 2015 and was a finalist for the National Book Award. Stinks of censorship to me.
The Discard stamp doesn't mean a lot.
Our public library system acquires books, puts them into circulation, tracks how much interest there are in them, and then regularly makes decisions to retire older books that have little uptake or signs of extraordinary wear. When that decision is made, they usually stamp them "Discard", offer them for sale for a $1 or $2, and use the space freed up for newer acquisitions.
Our public library system is more oriented toward putting lots of books into lots of hands than it is toward creating a collection or a reference source.
I've got a fair number of books and CDs that way. After enjoying them, I keep some, and donate others.
If you have little kids in your extended family, it is a great way of getting them lots of children's books, at a very reasonable cost.
On the subject of the thread, and with my Moderator hat on, I would caution that Photrio is at best an awkward place to discuss the religious, social and political arguments that surround the subject of depiction of child nudity.