File name of image: Make sure to include keywords in the file name. So if you are targetting format usb,then name the file as format-usb.jpg. Do not use underscores. Even Matt cutts has previously confirmed that dashes are better than underscores
Image Alt tags: This is good for usability and good for SEO as well. Make sure to use descriptive alt tags and include keywords.
Image search results do not monetize well since google shows the results in an iframe. Solve that problem by adding the following code to your page. Now when a person clicks on a image search result, he will directly come to your site like normal search.
<script language="JavaScript" type="text/javascript">
if (top.location != self.location) top.location.replace(self.location);
</script>
Here is a video from Google that provides more detail about image search. It is 15 minute long, so watch it in your spare time.