In your email client (such as Microsoft Outlook) as Jason states images arnt displayed by default - usually you should see a little alert message below the emails subject outlining "Click here to download pictures - To help protect your privacy, Outlook prevented automatic download of some pictures in this message."
I am attaching a screenshot for my Outlook 2013 client software.
All you would do is click where it suggests on the alert area...or....right click on one of the image placeholders in the email and there should be an option to "Download Pictures".
Chris