Use two Input nodes to programmatically pass in images, extract the color and opacity of the images separately, and use an unlit material with tone mapping disabled to achieve the exact colors. The full code and Xcode project can be found on GitHub https://github.com/Lightning-Lion/StereoImages.

I need to obtain the 2D position of a 3D point on the left eye screen, which will be used for running a specific machine learning algorithm on the left eye's camera frame, not for rendering content. Therefore, Reality Composer Pro is not helpful for this use case.