Default width is 300. (A width greater than 500 will likely end up off the page on smaller screens)
Default height is inherited based on width and size of image.
Default external condition is no. Acceptable true switches are: 1, on, true, y, yes
NOTE: External images do NOT follow the width rules, be sure to enter an appropriate width or your popup box size/border may be too small or too large.
link= & alt= cannot be used together. You can either specify a different page for the page to go to or a different text but not both.
Examples
{{Image popup|No_pic image on mouseover|No_pic.jpg}}
{{Image popup|External image on mouseover, red background, too small of a box|http://upload.wikimedia.org/wikipedia/mediawiki/a/a9/Example.jpg|xtrnl=y|bgcolor=red|width=200}}
{{Image popup|External image on mouseover, red background, too large of a box|http://upload.wikimedia.org/wikipedia/mediawiki/a/a9/Example.jpg|xtrnl=y|bgcolor=red|width=500}}
