How do I transfer an OpenCV image to a material using the prebuilt free version?

There is a lot of stuff about doing animation I just want to start with an image and work from there.

The “prebuilt free version” of … what? Unreal Engine?
Unreal Engine isn’t “free” in any version, although there are revenue minimums under which you pay nothing, which might be what you mean?
Or free version of OpenCV? OpenCV is open source, I don’t know of a non-“free” version.

Anyway, you can “add C++ class” in Unreal, no matter what version you’re using. E g, the downloaded-built engine still has this feature. Add a C++ class, perhaps using a template that “includes an external library,” and have that include OpenCV. Make your C++ class provide a texture or bitmap or something out to the rest of the engine, which you can use however you want.

You might also want to look at the Victory plugin from Rama, it may have some helper functions, like Victory_LoadTexture2D_FromFile().