Photograph manipulation or photograph alteration is the modification of an otherwise genuine photograph. Some photograph manipulations are considered to be skillful artwork, while others are considered to be unethical practices, especially when used to deceive. Motives for manipulating photographs include political propaganda, altering the appearance of a subject (both for better and for worse), entertainment and humor.

Depending on the application and intent, some photograph manipulations are considered an art form because they involve creation of unique images and in some instances, signature expressions of art by photographic artists. For example, Ansel Adams used darkroom exposure techniques to darken and lighten photographs. Other techniques include retouching using ink or paint, airbrushing, double exposure, piecing photos or negatives together in the darkroom, and scratching instant films. Software for digital image manipulation ranges from casual to professional skillsets. One of these, Adobe Photoshop, has led to the use of the term photoshop, meaning to digitally edit an image with any program.

Photo manipulation dates back to some of the earliest photographs captured on glass and tin plates during the 19th century. The practice began not long after the creation of the first photograph (1825) by Joseph Nicéphore Niépce who developed heliography and made the first photographic print from a photoengraved printing plate. Traditional photographic prints can be altered using various methods and techniques that involve manipulation directly to the print, such as retouching with ink, paint, airbrushing, or scratching Polaroids during developing (Polaroid art). Negatives can be manipulated while still in the camera using double-exposure techniques, or in the darkroom by piecing photos or negatives together. Some darkroom manipulations involved techniques such as bleaching to artfully lighten or totally wash out parts of the photograph, hand coloring for aesthetic purposes, or mimicking a fine art painting.

In the early 19th century, photography and the technology that made it possible were rather crude and cumbersome. While the equipment and technology progressed over time, it was not until the late 20th century that photography evolved into the digital realm. In the 20th century, digital retouching became available with Quantel computers running Paintbox in professional environments, which, alongside other contemporary packages, were effectively replaced in the market by editing software for graphic imaging, such as Adobe Photoshop and GIMP. At the onset, digital photography was considered by some to be a radical new approach and was initially rejected by photographers because of its substandard quality. The transition from film to digital has been an ongoing process, although much progress was made in the early 21st century as a result of innovation that has greatly improved digital image quality while reducing the bulk and weight of cameras and equipment.

Ansel Adams used darkroom exposure techniques, burning (darkening) and dodging (lightening) a photograph.

Whereas manipulating photographs with tools such as Photoshop and GIMP is generally skill-intensive and time-consuming, the 21st century has seen the arrival of image editing software powered by advanced algorithms which allow complex transformations to be mostly automated. For example, beauty filters which smooth skin tone and create more visually pleasing facial proportions (for example, by enlarging a subject's eyes) are available within a number of widely used social media apps such as Instagram and TikTok, and can be applied in real-time to live video. Such features are also available in dedicated image editing mobile applications like Facetune. Some, such as FaceApp use deep-learning algorithms to automate complex, content-aware transformations, such as changing the age or gender of the subject of a photo, or modifying their facial expression.

The term deepfake was coined in 2017 to refer to real images and videos generated with deep-learning techniques. The alterations can be created for entertainment purposes, or more nefarious purposes such as spreading disinformation. Fraudulent creations can be used to conduct malicious attacks, political gains, financial crime, or fraud. More recently, deep fakes superimposing the faces of celebrities and other persons onto those of pornographic performers for the purpose of creating pornographic material has become prevalent; deepfake pornography has been criticized due to issues with lack of consent.

Raw astronomical images of celestial objects are usually generated from data provided by complex digital cameras. Raw images include binary (black-and-white) or grayscale data generated in response to infrared or ultraviolet or other energy lying outside the visible light spectrum—requiring people to make technical decisions for how to transform the raw digital data into colorized pictures for human viewing. For example, in images from the James Webb Space Telescope and Hubble Space Telescope, the usual transformation is to use blue for the shortest wavelengths, red for the longest wavelengths, and green for intermediate wavelengths. Both scientific accuracy and visual appeal contribute to the decisions, for both enabling accurate analysis by scientists and providing visual interest for the public. Also, science visualization specialists sometimes stack images together, stitch observations from different instruments, enhance contrast, and remove artifacts.