Are you on a Mac and using Safari? I'm guessing that your browser isn't using the Moodle HTML editor which makes placing images REALLY easy. If this IS your situation, you might want to
download the excellent (and free
FIREFOX) browser which lets you use the HTML editor... You could use
IE, too, but who wants to?
.
If you want to code HTML by hand (and not use the editor), your best bet is to go to uploaded file list, hover over the jpg's name, and copy its moodle link. Uploaded files look like this: /moodle/file.php/4/bigfish.jpg. Once you have the real link name, you can use the img src html code to paste it into various places in Moodle.
Good luck,
Tom
p.s. If I've guessed wrong on the OS and browser, you might check the site settings and the user settings to ensure that you've made the HTML editor available to you.