Spot the difference is a type of

puzzle A puzzle is a game, problem, or toy that tests a person's ingenuity or knowledge. In a puzzle, the solver is expected to put pieces together ( or take them apart) in a logical way, in order to find the solution of the puzzle. There are differe ...

where players must find a set number of differences between two otherwise similar images.

Description

Spot the difference games are found in various media including activity books for children,

newspaper A newspaper is a Periodical literature, periodical publication containing written News, information about current events and is often typed in black ink with a white or gray background. Newspapers can cover a wide variety of fields such as poli ...

s, and

video game A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device) to generate visual fe ...

s. They are a type of

where players must find a set number of differences between two otherwise similar images, whether they are illustrations or photographs that have been altered with

photo manipulation Photograph manipulation involves the transformation or alteration of a photograph. Some photograph manipulations are considered to be skillful artwork, while others are considered to be unethical practices, especially when used to deceive. Mot ...

Solving techniques

Visual comparison A visual comparison is to compare two or more things by eye. This might be done by placing them side by side; by overlaying them; by alternating an image or by presenting each image to a separate eye. Such comparisons are the first stage in a chil ...

may be used to solve the puzzle. The solution to the puzzle is often listed nearby or in an accompanying answer page of a puzzle book. Additionally, one can cross one's eyes and merge the two pictures into one, in the much the same way as when viewing an

autostereogram An autostereogram is a two-dimensional (2D) image that can create the optical illusion of a three-dimensional (3D) scene. Autostereograms use only one image to accomplish the effect while normal stereograms require two. The 3D scene in an a ...

picture. The differences will appear to blink in and out of one's vision. This is a very effective method of solving these puzzles.

Overlay

A way to solve a spot the difference puzzle is to digitally compute the difference pixel by pixel. This requires both images to be perfectly aligned. In the presence of distortions, e.g. when taken from a photo, the

correspondence problem The correspondence problem refers to the problem of ascertaining which parts of one image correspond to which parts of another image, where differences are due to movement of the camera, the elapse of time, and/or movement of objects in the photo ...

has to be solved before overlay is possible. To compute a pixelwise image difference

p_1-p_2

an inverse version of the first image

1-p_1

can be overlayed with 50% of the other, i.e.

\frac(1-p_1)+\fracp_2

Description

Solving techniques

Overlay

See also