Hi there, maybe you misunderstood. My explanation was relevant because the issue is independent of pretty photo.
The reason why it is showing the name of the file is because when you are calling $Image you are calling the title of the images that SS automatically assigns based on the name the image when uploaded. In SS3 gallery the description field is generated by the GalleryImage class and not Image class. The answer lies in how your controls are being used.
So Try this...based on your code:
<% control getGalleryImages %>
<div style="position:absolute; top:0; left:0; z-index:100000">$Description</div>
<% control Image.SetWidth(928) %> <img src="$Link" <% end_control %> alt="$Description" /> /// Alt tag is outside $Image and now uses the Description of getGalleryImages
<% end_control %>