Handmade rag paper used for paper paintings and illustrated manuscripts may contain randomly distributed inclusions of uneven fibres or bits of extraneous materials. At times the paintings may also exhibit paint loss. Ordinarily these internal defects in paper are not visible, and lacunae in the paint may also not be discernible if it is repainted perfectly. It is very unlikely that the extent of these inclusions or paint losses will be similar in two different paintings; therefore, the shape and size of the hidden defects and their spatial distribution can be used as the fingerprint of a painting, as it is impossible for even a master forger to replicate the internal paper structure. Hidden defects in any translucent object such as paper paintings become visible when it is illuminated from the backside, and the painting can be photographed along with the hidden defects by illuminating it from both sides. The intensity of the lights used and their placement may vary from painting to painting depending upon the thickness of the paper and the paint used. To determine the correct combination and intensity of these light sources is the very essence of this technique. The improvised method presented here is very simple and requires commonly used photographic equipment. Several miniature paintings were photographed by illuminating them from both sides, and the pattern of hidden defects in each painting was found to be unique.