I always take a "blank" photo in between properties. That way, I know that the blank photo is a separator. I just take a pic of the inside of my camera bag & it shows up dark. Works great for me.
I used to do it that way until I bought the BEST camera for doing bpo's the SONY FD MVC-FD75. You can buy one on ebay under $100. It uses floppy disk....So each property I shoot has its own labeled disk and I never have to resize because of its low quality under 1 mega pixel.
This camera is my hot tip for the week....spend a $100 you'll be glad you did.