I'm using some images (mainly as backgrounds, but otherwise I may as well) for my a website I'm making.
No. Your website can be considered a 'medium through which you share the image', so you can use and share the image, while not sharing your own code.
But you DO have to share the image, and share any modifications you make to it. So if you're using a forest photo and stylize it or draw creatures in, you MUST allow other to use that image. And of course, you have to include proper attribution, so it'll affect your design/layout/sitemap a bit.