The alt="" attribute is for entering a description of the object when a browser doesn't show the actual image.
Example: alt="logo image"

If you want a better description for SEO (and for a popup label in browsers) use the title="" attribute
Example: title="TalkGraphics.com is a place for like-minded individuals to chat about graphics software, website design and more"

Both of these can be filled in using Web Properties>>Image[tab] (for Alt text) and >>Mouse-over [tab] (for Title)

The source then looks like this:
<img class="xr_ap" src="index_htm_files/1.png" alt="logo image" title="TalkGraphics.com is a place for like-minded individuals to chat about graphics software, website design and more" style="left: 399px; top: 14px; width: 287px; height: 208px;"/>