Checking for the input name in the POST variable when using an image type, the PHP looking for the name could not find that input object.
Internet Explorer as well as some other browsers, pass the x and y of the image you used for submitting your form instead of the input name. To detect these with PHP, you can check for
isset($_POST['image_x']) || isset($_POST['image'])
if either is true, you can continue to process. You may also note that the browser has converted what would have been image.x into image_x. The period character is swapped out.
Now you should be able to have your input be detected in all major browsers.