How to checksum an image or bitmap directly in memory

[mdepot]

I have a situation where I am repeatedly capturing a region of the screen and feeding it into Tesseract OCR.  Since the OCR is a relatively slow operation, I would like to create an in memory cache of the ocr results.  An ideal hash key for this cache would be a checksum of the captured image.  With this I could capture the region, checksum it, and then only if I don't get a cache hit I would write the image out to disk for external OCR.

Now I know I can do this by saving the captured image out to disk, and then summing the disk file with _Crypt_HashFile().  But that's still slower than I would like, and it shouldn't be necessary.  Ideally, it should be possible to checksum the image data directly in memory so I don't have to go to disk at all.  In order to do that, I need a way to dump a representation of the image into a string  (or some equivalent).  Then I could use the _Crypt_HashData() function against that string to create my cache hash key.

Googling around I found an article here that shows a way to convert an image object to a byte array using System.Drawing.  This was the closest thing I found to what I'm trying to do.  I don't know if that method could be used from within AutoIT, or if perhaps there may be a better way I don't know about.  If someone could give me a shove in the right direction it would be a big help.  Thanks!

Edited August 12, 2018 by mdepot

[jdelaney]

PixelChecksum

If different, in a loop, then do the tesseract call?  It would be directly checking the pixels, rather than screenshoting them.

Edited August 12, 2018 by jdelaney