Right, I understood.
The easiest place to start would probably be with the HTML. You would first create the form with a checkbox related to each image.
Code:
<input type="checkbox" name="image1" />
The user would then select all the images he wants.
Next you would use jQuery to loop over all of checked input[type='checkbox'] elements . You would then take the name attribute of the elements, concatenate them and then set them equal to the value of the textarea.
Finally, email it off using some PHP.
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