Checking a checkbox by clicking an image with changing image opacity

[EDSki]

i have a image with checkbox, i used this code for Checking a checkbox by clicking an image...\[code\]<label for="img1"><img class="img" src="http://stackoverflow.com/questions/15740206/myimage.jpg" /></label><input type="checkbox" class="chk " checked="checked" id="img1" name="img1" value="http://stackoverflow.com/questions/15740206/0" />\[/code\]its working fine, my question is, i want when checking check box above image opacity will be \[code\]0.5\[/code\] or display a extra \[code\]div\[/code\] over this image and when Un check above image opacity return to \[code\]1.0\[/code\] or remove that div if we use div, any idea.???thanks