In that case I guess you can set the height of the ul.pictest li to the needed image-height, and give the .pictest ul li their own height for the submenu links.
Remaining problem though: if the visitor is changing the font-size of the browser, the submenu items can overflow the fixed height.
To avoid that, you can set the images as a background-image (each with a class in the main list items), and draw some extra px in the bottom of the image (with 50px extra no problems, I assume). Or give a background-color for the area where the image is ending. Then you can take a min-height for the main li's instead of a fixed height.