Pictures don't lack demographic targeting. You can make a lot of demographic assumptions from the content inside of a picture.

Example: facial recognition says that this blob with eyes in the photo is a child. Flag may have signed up Babies R Us as an advertiser. Based on the notion that it's a baby on the front of the photo the back as should be for formula, college funds, or diapers.

The tricky part is building up the tooling to automate that process. But hey, most of that exists in the wild already.