Widely-used command-line tools that allow manipulation and conversion of image files in batch
Free utility from Adobe for converting camera RAW files to the Adobe Digital Negative (DNG) format (https://helpx.adobe.com/photoshop/using/adobe-dng-converter.html). DNG files are likely better suited for preserving "unprocessed" image data than camera RAW files, as they are usually stored in a proprietary, manufacturer- or model-specific file format. DNG is a specification maintained by Adobe, but it is fully published and available for use royalty-free. See https://www.loc.gov/preservation/digital/formats/fdd/fdd000188.shtml for further information about the DNG specifications.
Open source software used for converting audio and video data (https://ffmpeg.org/)