Files go in a structure as follows
- game folder often called bin but doesn't need to be
- downloaded or compiled html file for the game
- resources (folder)
Okay, for custom images.
1. Open Options, Game options, Display
2. Scroll down to Images, enable images which will then show the pack selection options ("but why, I don't want imagepacks")
2a. The above toggle also makes it show a new secondary toggle to hide the imagepack images if you only want to see custom images
3. Open a slave description and go to customize tab
4. There is a field to assign custom images, it assumes all files will be in resources or subfolders in resources so the inputs are just imagename or subfolder/imagename and then select the file type, spaces in the file name and folder names appear to work for me but I wouldn't include periods or other punctuation.
I've had people get tripped up by the need for step 2 and 2a as the select a custom image box is still present on the customize tab even when the image display is disabled.
Also it is fiddly on android / mobile as some browsers or incognito mode have reduced file system priveledges so I think I had to use chrome in normal not incognito mode to play if i wanted to save or load from files or use external images.