Mathpix is a great idea, executed well:

The Mathpix desktop app allows users to take screenshots of math equations and paste the extracted Latex, all with a single keyboard shortcut.

For example, I wrote this on a piece of paper and took a picture of it:

And Mathpix put the following text on my clipboard:

\sum _ { i = 0} ^ { n } i = \frac { n ( n + 1) } { 2}

Which is exactly right:

$$\sum _ { i = 0} ^ { n } i = \frac { n ( n + 1) } { 2}$$

Mathpix can grab anything that is displayed on your screen.

The Mac app is free on the Mac App Store and there is a corresponding iOS app which is free with in-app purchase.