how to stop attacks from images or tags

Lets consider i have a domain named http://ift.tt/V4rFOk. Some people are attacking my website by calling it using millions of image tags, like

<img src='http://ift.tt/V4rFOk' >

<img src='http://ift.tt/V4rFOk' >

<img src='http://ift.tt/V4rFOk' >
 so on
</body>
</html>

This activity sending me too much spam traffic and my server is getting down. iam unable to stop/filter those requests, Please let me know what kind of attack it is and how to prevent it?

i have tried to stop the requests which consist image/png, image/jpg in ACCEPT request headers. it worked for latest versions of browsers.But the lower versions of IE is not supporting for the ACCEPT parameter properly, it always sending / in ACCEPT requests headers.