pandoc --extract-media ./myMediaFolder input.docx -o output.md
From the manual:
--extract-media=DIRExtract images and other media contained in or linked from the source document to the path DIR, creating it if necessary, and adjust the images references in the document so they point to the extracted files. Media are downloaded, read from the file system, or extracted from a binary container (e.g. docx), as needed. The original file paths are used if they are relative paths not containing... Otherwise filenames are constructed from the SHA1 hash of the contents.