Just had a belated reply back from Andy, see below. I think it is self explanatory.
Colin
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Hi Colin,
Sorry for the very late reply, I missed this email in my inbox somehow.
Technically there isn’t, however longer names can cause issues with some plugins as well as SEO.
Ideally they would be below 65 characters, but I would try and keep it as low as possible. Also, the character count adds to the overall URL, so the domain, plus the folder(s), plus the filename, and again that can cause issues for some plugins and database records if that gets too long.
What it doesn’t like is special characters or spaces, this can cause issues when the filename is sanitised, also capital letters can lead to future compatibility issues.
Good SEO usually means the filename would be relevant and unique also, so lots of files called image1.jpg isn’t idea, usually changing them to something relevant to a post or article helps, so something like model-steam-powered-boat-mar24-1.jpg, model-steam-powered-boat-mar24-2.jpg etc.
So in an ideal world:
-Lower case,
-No spaces
-No special characters
-Avoid really long filenames
WordPress does a good job of working with most filenames thrown at it, but the plugins that run over the top of it aren’t always as forgiving, so sticking to the above will help prevent issue when uploading, and with future compatibility.
Cheers,
Andy