Adding a border to an image to use as texture

Dear all,
I am trying to add a border to an image on the fly and use it as texture

I am using the compositor but for now I succeeded using the “Compositing Nodes” editor.
I work with this setup



I have tried the “Texture nodes” editor but I am not able to overlay the two images properly (the black background and the code)

Thus I am asking:
Is there a way to pass the result of “Compositing Nodes” to “texture nodes”?
there is a way to achieve the same thing on the texture node?

I would like not to save images on the pc, but to have simply to upload the code image and let blender prepare the texture.

Save the output? Use that rendered file as a texture. The compositor is a post production tool, used after rendering the 3D elements.

I would prefer not to save anything on the pc, creating the image on the fly. I tried using “Render result” as imput but I get an error “Can’t load image”