When the chapel was restored in 1990 the biggest donors to the project (donating a whopping $4.2 million) were a Japanese television network. In return, they received exclusive rights to photograph and film inside and quickly banned any professional photographers from taking pictures. Although they didn't mind if tourists took photos, the Vatican guards decided to enforce the rule on everyone because it was impractical to differentiate between a normal visitor and who was a professional photographer. The Japanese network's exclusive contract has expired now but the rule persists. If you try to take any images in the Chapel Vatican, security is authorized to make you delete them.