Bug why is there a box around my img and how can I get rid of it?

Here is a straight <img/> image is guitar notice there is no box around the img

simple <a> this is a simple anchor tag

<a><img /> where did the box around the img come from?

<div><a>xxx<img /> </a> </div>

how come text-decoration:none turned the underline under 'xxx' off but left it around the image?