What tools are available for image processing with Red and Rebol?

 For Rebol 2 we have: https://github.com/ldci/OpenCV3-rebol. 

This version is old (2015) but still operational. There are around 600 basic OpenCV functions available with Rebol 2.

For Rebol 3, there's the fabulous module created by Oldes: 

https://github.com/Oldes/Rebol-OpenCV

Although incomplete, this module is fanatstic as it allows you to use the latest versions of OpenCV on different X86 or ARM64 platforms. 

You'll find a lot of samples here: https://github.com/ldci/R3_OpenCV_Samples

For Red, we have https://github.com/ldci/OpenCV3-red, which is still active. Although written more than 10 years ago, the code is compatible with the latest versions of Red (0.6.6).

And of course for Red, we have RedCV: https://github.com/ldci/redCV. Most of the code is written in Red/System and offers over 600 basic functions or routines for image processing with Red. 

With the exception of the Oldes code, I'm the only one to maintain all this, and I'm not sure that many people other than me use these codes. In any case, it has enabled me to write some very nice professional applications used at R2P2 (https://uniter2p2.fr).