Once you get that javascript working. You can use the css class that gets added to your image when the checkbox is checked to add more css to the line image
If it's not a sibling, then you will need to do it with jQuery. If you give us a preview link to tinker with, we can give you the exact code you need to drop into your page.
Once you get that javascript working. You can use the css class that gets added to your image when the checkbox is checked to add more css to the line image