Make sure the photo is not on 'heavy matte' stock. Glossy is better. Too much matte looks like a checkerboard to the scanner. You can test this by reflecting light off the photo at an angle. The clearer the reflection looks the better.
Shadows are also bad.
If you aren't on the picture you won't be in the scan. Don't select a photo because of your clothes. They won't make the scan. We just do faces. Typically from the top of the head to just below the chin.