Make sure that if you use images, you NEVER. EVER. EVER use .JPG.
OH MY LORDY LORD. I just uploaded a fully illustrated version of my game The World Ends Today, I Think after months of playtesting. I thought it was good. Great. Perfect. No bugs. No nothing. But then, once I published it, some of the images weren't rendering.
But... Why though?
I have no idea how it happened, but some of my files were .JPG instead of .jpg. My computer when I was testing it straight from the HTML file didn't bother about this difference at all. But it does when you publish.
I had to scout out for all of those rogue images because the extension didn't show up in the file name. I used the inspect tool on my published game to see which specific images weren't showing up. Then I converted them to .jpg.
A cautionary tale. I hope no one has to go through this pain ever again.
I spent two nights a week ago staring at a jpg that wouldn't load. Except that it was actually a jepg or some sort of nonsense extension. Time well spent...