Possible Clues:

• Something to take off in front of a camera
• Shutterbug accessory
• Cause of some missed shots
• You can't leave it on when you shoot
• It's a measure of the print that's endless in exam for agency - the view would be better without it!
• It should be removed before shooting
• Item a photographer might forget to remove
• It's protective for cameras
• Accidental 'subject' of certain snapshots
• Type of camera cover