Hi there,

If you are running the most recent version of windows, which is the windows creators update version 1703, and have the current version of nvda

which is 17.3, section 9 of the users guide gives detailed instructions about the windows 10 OCR feature and how to set things up. If you are running an earlier version of windows such as 1607, or NVDA version 17.2 or prior, I believe there's a tutorial on how to use the NVDA OCR add on at
 Http://www.accessibilitycentral.net
Hope this helps.

Tony