If they appear in-line in the mail message, just right-click on them
and select "Save picture as..." and select a destination and give it
a name.

If the pictures are in an attached file, download the file to your
computer.  If the attached file is an "archive" like a .zip file,
then you will need to extract the files from the archive before
you can use them.

-michael

"The wastebasket is our most important design
tool--and it's seriously underused."