Is there an OCR software that can convert a graphical image (in PNG, GIF, TIFF, PDF... format) of a mathematical formula into the corresponding TeX markup?
Yes. There is one that I knew.
More details, see this link.
The Mathpix app can convert pictures of printed and handwritten math and convert it to LaTex. The new Mathpix desktop app that was recently released lets you take a screenshot of the equation on your desktop and copies the LaTex to the clipboard so you can just paste it into your LaTex/markdown editor.