There are very few good Image-Menu for Joomla and the WMT Dock Menu Gallery is the best of all.
The commercial version, for a very small fee, offer a lot of customization and perfect integration with the core Joomla menu system.
You can control the size, magnification, spacing, etc. for every image in every menu.
Horizontal or vertical menus and much more.
The support from Developers Team is very fast and very professional.
Only drawback: I's impossible to keep the "HIGHLIGHTED" state for a single image during navigation........but this feature is currently unavailable in any image-menu system in the JED.