Camera Obscurer

A character takes a picture with a camera, and the photo develops, revealing that the picture taker had his/her finger(s) on the lens or left the lens cap on, obscuring the intended target of the photo. Bonus points if the camera in question is a SLR camera, because the viewfinder uses a mirror and prism to show the exact view through the lens, requiring a truly monumental level of stupidity. Usually fully justified when the camera in question in a vintage viewfinder camera.

This can still occur in the age of digital cameras, if the person has only a limited opportunity to photo their intended target and can't afford the time to review their settings before taking the shot.

Not to be confused with the Camera Obscura. Nor should it be confused with the Camera Obscura, from which this trope derives its name.

Comic Books

 * Ambush Bug did this in one of his 1980s miniseries.

Film
"Neville Bell: Oh no, you can't take my photograph. Sue Charlton: Oh, I'm sorry, you believe it will take your spirit away. Neville Bell: No, you got lens cap on it."
 * Crocodile Dundee:


 * Sky Captain and The World of Tomorrow: Polly Perkins spends much of the movie with only one frame left on her only roll of film, and wants to save it for a truly awesome photo. In the film's denouement, she decides to take a photo of, only for Joe to look at her and say "Lenscap."
 * Annoyingly, she could still have taken that picture. With the lens cap on, there would have been no light - meaning no exposure. Being that the while movie is 40's retro technology, that was probably a manual camera. If she didn't advance the film, she could have taken the cap off and shot that frame again.

Literature

 * In Discworld, Rincewind uses a camera flash to defeat an Eldritch Abomination and later finds out that he only has a photo of his thumb to show for it.
 * In the original Cheaper By the Dozen book, the father of said dozen children wants the removal of his children's and his own tonsils filmed. Since he wants to direct the filming of his own tonsil removal, he stays conscious during the procedure, and suffers great pain because of this. The pain turned out to be all for naught when the cameraman revels he accidentally left the lens cap on.

Live Action TV

 * There was an episode of CSI where they started trying to identify the taker of a photograph by the print of the picture of his thumb he left over the lens (until they decided they could get more information by looking in the reflection of the subject's eyes. That episode was worrying on so many levels.)
 * Mad TV: one part of an Average Asian skit ends with this.

Music
"Too bad we left the lenscap on the camera by mistake/'Cause grandpa weren't too happy about the second take"
 * From Heywood Banks' "Trauma to the Groin":

Newspaper Comics

 * There is a running gag in the Curtis comic strips where Curtis' barber claims to have met someone famous. When asked to show proof, he will inevitably produce a photograph of himself with his arm around the celebrity... except that the "celebrity" will be obscured by a finger.

Real Life

 * That famous picture of George W. Bush looking through the binoculars and they have caps on (which may or may not have been manipulated; undetermined according to Snopes).
 * A similar picture exists with Bill Clinton, of course.

Video Games

 * The Sims 3 has this occur from low photography skill, making the photos near worthless.

Western Animation

 * Wile E Coyote and The Road Runner: Coyote uses a gun disguised as a camera, only for it to literally backfire because he left the lens cap on.
 * Happens on Dexter's Laboratory, when Deedee takes photos of his lab and plans to show it to their mom. Fortunately for him, his lab is barely seen due to Deedee's fingers being in the way.
 * Jonny Quest episode "The Sea Haunt": Hadji tries to take a picture of the title monster but all there is on the photograph is a fingerprint.
 * In The Flintstones, Fred and Barney capture the legendary whale Adobe Dick and Barney takes a photo of it before it escapes. Unfortunately, the picture was covered by Barney's thumb, which was a Running Gag earlier in the episode.
 * The Invader Zim episode Megadoomer had this happen at the end, with the Humongous Mecha's Invisibility failed and Dib tried to take pictures of it.
 * When SpongeBob SquarePants made a movie of Mermaid Man and Barnacle Boy, cameraman Patrick left the lenscap on so he wouldn't misplace it.