tex4ht supports saving math as images in LaTeX to HTML conversion. by default, it uses png, but it can be configured to use svg instead. if you use
tex4ebook, which is based on tex4ht and can export directly to epub and epub3, you can try
this build file.
personally, I would go with epub3 and use mathml, because image math is horrible no matters if it is bitmap or svg. downside is poor reader support, but nothing pushes their creators to change that if there are no epub3 math books.