We recommend that a stuck photo not be removed from the glass. This can cause substantial new damage to the photo - which may or may not be repairable. The best approach is to scan the photo right through the glass in high resolution, then reprint it.
From a photo restoration perspective, it is far easier to remove any incidental glare caused by the scanner than to restore the new damage you may create when you remove the image. A severe tear across a face may be disastrous.
Even if you want to try to remove the image, please scan it in high resolution (300 dpi+) before you make the attempt. That way, if you fail you have a scan taken before you damaged the image.
I hope this helps. We see this issue all the time, and the scan through glass method only fails when the frame is of such a size, shape or glass condition that a good scan is impossible. If a scan is possible, try this route.
Jeffrey Makoff
DigitalCustom