save as dialog or context menu

Hi. I'm looking for a way to have a button in a page which could replace the save picture as fonction, the same as the one available when clicking on a picture. So the save as dialog would open to save the picture.

OR

Have a context menu to open when clicking on an image to have the dialog open.

It has to be client-side cause it would be on a cd-rom.

Ideally, this would be cross-browser-platform.

Any idea or link to any ressources.

Thanks