Hi,
It's not going to work with the <input type="image">
tag. This is really a submit-button with an image instead of a
button.
Radio-buttons are one option. But a user could only select
one image from a group, so if they are supposed to select two
images, you would have to show all images twice.
The better option would be to use checkbox fields, and have a
javascript function that verifies that only two images are
selected.
An option that avoids the radio or checkbox inputs is to have
a javascript onlick function for each image that enters the name of
the image into a (or one of) hidden text field(s).
I would go with the checkboxes, and if necessary you could
hide the actual checkboxes with CSS by making them invisible or
hidding them behind the image.
cheers,
fober