Dear Nadina, The inks used for dyes are usually very unsaturated in chemical terms.(Visible colour is associated with this unsaturation) Over time inks get decolourised via reactions across the double bonds. Nevertheless, although the colour is hardly visible anymore, there are usually lots of double bonds still left. so what you need in order to detect the remnants of now colourless ink is some way of detecting double bonds without destroying the photograph. An ultraviolet light should do it. You may be able to access one via a local school or university science department, a bank, a library or even restaurant (repel insects). Gail of New Zealand