To add to Scotty's clarification it effectively inserts title="" into the image tag after the alt="???....????" attribute. The empty string within the quotes prevents I.E. from displaying any pop up text.

e.g.
<img class="xr_ap" src="stove-home_htm_files/10.png" alt="Harold log stove" style="left: 173px; top: 223px; width: 144px; height: 159px; " onmousemove="xr_mo(this,0)"/>

becomes

<img class="xr_ap" src="stove-home_htm_files/10.png" alt="Harold log stove" title="" style="left: 173px; top: 223px; width: 144px; height: 159px; " onmousemove="xr_mo(this,0)"/>

It is a very cumbersome work around but for pages that are not updated too frequently it may be an acceptable solution.