Im sure I had something like this in the menu guide I made in the wiki.
From the source:
PICTURES
pic - sets the image file
hoverpic - image that appears when you put the mouse above the image
selectedpic - image that appears when you click the image
COMMANDS
doubleclick - command to do when you double click the image
command - command to do when image is clicked
SIZES
picwidth - the width of the pic
picheight - the height of the pic
hoverpicwidth - width of hoverpic
hoverpicheight - height of hoverpic
POSITIONING
xabs/xleft/x - position of the image where 0 is the leftmost edge of the screen
yabs/ytop/y - position of the image where 0 is the top part of the screen
xcent - x position of the image relative to the center of the screen
ycent - y position of the image relative to the center of the screen
xright - x position relative to the right of the screen (0 is the rightmost edge)
ybot - y position relative to the bottom (0 is the bottom)
xrel - x position relative to the last widget you made
yrel - y position relative to the last widget you made
ALIGMENT
halign - horisontal aligment. can be left, center, and right
valign - vertical aligment. can be top middle bottom
There are a lot more values that can be set, but they dont apply to the images.