Double click on Control Panel on your desktop, then Default Programs,
then click on Associate a file type or protocol with a program. Wait for
the list to load then go down the list to .jpg. Make sure the entry in the
Current Default program for it is a program able to open .jpg files. I use
Windows Photo Gallery. If you need to change the program, click on
..jpg, then Change Program, then a suitable program, then OK, then Close,
then close the Default Programs window. This should select the correct
program for opening the file outside Windows Mail; if it doesn't also select
the correct program for use inside Windows Mail, you'll need someone else
to take over helping you.
To make sure Windows Mail will try to open such attachments, click on
Tools, then Options, then Read. If there is a checkmark in the box before
Read all messages in plain text, click on this box, then Apply. Click on
Send, then the HTML Settings for Mail Sending Format. If there's no
check mark in the box before Send pictures with messages, click on this
box. Click on OK, then Apply, then OK. Restart Windows Mail and try
to open the email again.
Also, is the email that came in at least as big as the picture file?