Creates a popup image in the HTML output.
If you are using the HTML output facility, and HTMLSTYLE is set to 'overlib', then a link is added to the <map> section of the HTML so that when you move the mouse pointer over the the (weathermap) link, a box will pop up containing the image that you specify. Typically used to link to historical data in your network monitoring system.
You can also specify more than one url, in which case the images are 'stacked' one after another in the popup box.
If a NOTES line is also specified for a link, then the image specified here appears with the NOTES text underneath it.
It is also possible to specify the OVERLIBGRAPH for the 'in' and 'out' halves of a link individually, using INOVERLIBGRAPH and OUTOVERLIBGRAPH.
You can influence how Weathermap positions the popup box, using the OVERLIBWIDTH and OVERLIBHEIGHT keywords.