The usual format of an anchor is <a href="filename">text here</a>. We can replace "text here" with our IMG tag <img src="goback.gif">, and the picture will become clickable. So instead of:
click here to go back a page
click to go back a page.
Notice in the source for this page that the instructions are the SAME. Because both anchors have the same href= part, they both go to the same destination.