SRC tells where to get the picture that should be put on the page.
SRC is the one required attribute for <IMG ...>.
For example, suppose that the GIF file "../graphics/pumpkin.gif" is in the same directory as this page. We can place it in the page like this:
this code
produces this
<IMGSRC="../graphics/pumpkin.gif" ALT="pumpkin">
SRC is a hypertext reference, like the <A HREF="..."> attribute. The reference can be relative (like the example above) or it can be a "fully qualified" reference.