While adding pictures to a new group, "Dallas Market Center Spur", I realized that one of the pictures added may be the 500th picture on the website.  Once I finished, I looked in the database to see if the 500th record was reached and sure enough, 506 records existed.

So, I present to you picture number 500 on abandonedrails.com:

http://image.abandonedrails.com/?id=521

Not a particularly memorable photo, but a red-letter photo nonetheless.