Alright, right off the bat, you need to realize that there is an easy way to do this, and then two (in my mind) hard ways.
[Easy]
They scan the pictures using another program, and the PHP application scans whichever directory they want for new pictures every $x number of minutes, seconds, or milleniums, depending on their/your preference. This is...by far, the easiest, however, it may not be the type of integration that they're looking for. I'd go with this one personally, but again, may not be feasible in their minds, and gosh blasted, those darn customers are -always- right somehow.
[Hard #1]
You can create (or alter) a program to scan the pictures, and have it send the data to a PHP script which will receive the binary data and insert it into the database. Won't explain this one as much because the easy solution is still preferable.
[Hard #2] {Variation of #1}
You can also create a COM object to work in conjunction with the current scanning program that they would use. PHP can use COM objects surprisingly easily, and this would allow you to access the data this way or that. Again, won't get far into this, as you should still hope to go with the first.
Hope this helps. 🙂