Form with 2 pic gallery as radio? and submit button

I'm looking to build a form (as in the code below) which will allow the user to TWICE select an image from a database derived photo gallery (ideally a list of thumbnails with a mouseover enlarge) and then submit along with an email address. However, it seems that <input type="image" > submits the form immediately upon click. Suggestions on how to handle appreciated :)

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<form name="form1" id="form1" method="post" action="">

1.) Pick one from the following list of pictures:<br />
<input type="image" > <input type="image" > <input type="image" > <br />

2.) Pick one from the following list of pictures:<br />
<input type="image" > <input type="image" > <input type="image" > <br />

3.) Enter email for confirmation:<br />
<input type="text" name="Email" id="Email"> <input type="submit" >

</form>