Handling Image Links in Custom Theme

I’m converting a static page into a WordPress Site, and I’m having a hard time finding any guides concerning the structuring of image links. What I mean is how should I format the img src attribute? My current test site is uploaded at http://www.taylorp0994.net/websites/cincoschool/. I have all my images in a folder titled “img,” but when I reference them in index.php for my theme as I would in pure html they are broken. Curiously enough, the css image reference I use for my background image from the same folder works without issue. How should I reference static images in my php for a custom template, and as a side note, how can I reference dynamic images? I apologize for my newness to WordPress. Thank you for any assistance you may have to offer.