This function looks for JPEG signatures in any file you choose, and if it finds such a signature followed by valid data, then it extracts that data and saves it to an external file. Use this function to acquire JPEGs stored in a file of your choice, e.g. the JPEG previews from RAW files.
Use the Do not create copies of JPEG files option to prevent the function from creating duplicates of JPEG files if you accidentally use it on them.