ImageMagick

ImageMagick is published by ImageMagick Studio LLC under the ImageMagick License, which the project states is compatible with the GNU General Public License version 3. Version 7 is current, with 7.1.2 the stable series at the time of checking, and version 6 is listed as legacy with a porting guide. The magick command does the work that older installations spread across convert, identify, compare and other names. It reads and writes a very large number of formats, among them JPEG, PNG, GIF, TIFF, WebP, AVIF and Ultra HDR. Bindings exist for C, C++, Python, .NET and Node.js. The download page lists Windows installers for several architectures, a portable Linux AppImage and Homebrew on macOS.

Three jobs recur in forensic use. Identify in verbose mode lists an image's format, dimensions, colour space, bit depth and embedded properties, which goes into the notes beside the ExifTool output. Compare measures the difference between two images with a chosen metric and draws a difference image, which is how an examiner shows that a working copy is pixel-identical to the original or exactly where two versions differ. Convert to a lossless format such as PNG prepares an image for analysis without a second lossy save. Cropping, scaling and contact sheets serve presentation and are logged as commands. A difference map shows difference, not tampering: the interpretation of why two images differ, and whether that points to editing, belongs to an authentication tool and an expert. Lossy re-saving of evidence is avoided and the version used is recorded.