How about asking for a gallery specifically for images to be used in the image manipulation thread?
There are no doubt plenty of people in the same position as myself, in that they have a lot of images which they would not normally post (bland, uninteresting, poor composition etc.), which would probably be exactly what is required for the purpose of composition?
By having a separate gallery it would prevent the thread from being congested with people offering sample images as well as posting finished articles which may be lost.