This sounds interesting. I've added Comntr to my extensive blog post about static site comments [1]. [1] https://darekkay.com/blog/static-site-comments/
That's a great collection of libraries for a common problem that many people run into. If you're interested, I made a library for [1] hacker news comments on static sites. Let me know what you think.
You said SVG twice now, but I don't see what is obvious about it. It's an XML document that should be easier to figure out than a raster image format such as jpg or png.
Won’t it have to be converted to a raster image before it can be OCRd? Granted all you need to do is render it to a canvas but that’s an extra step on top of everything you need for a raster image, I’m not sure it’s easier .
And just rendering to canvas may be very tricky if the captcha is animated with css, i.e. it moves a bit and different parts of it appear at different times.