(Date: 17 July 2024.)
AUCTeX includes the preview-mode facility, which generates
embedded images of LaTeX fragments, typically mathematical
expressions.
This needs to be called manually, with preview-at-point.
Paul Nelson has written the package preview-auto, providing the preview-auto-mode.
This runs preview as needed after certain changes.
This is a very useful feature which works well alongside AUCTeX, on which it depends.
This package is available in GNU ELPA.