E. W. Hornung 
Camera Fiend [PDF ebook] 

Teenager Tony Upton, beset by a chronic case of asthma, has lived a sheltered, quiet life, tucked away from the world and left mostly to his own devices. But everything changes one day when what starts out as a humdrum trip to the doctor takes a rapid detour. Our hero takes a liking to an unusual camera he spies in a store window, and that chance sighting sets into a motion a series of strange and mysterious events.