Are you trying to send an image to an already exported Godot HTML project? I don’t know if it is possible to load image files at runtime with the HTML export, but if it is possible, this page on the documentation might help.
I have also written a proof-of-concept Godot plugin that can load resources while a game is running, though I have no idea if it works with HTML exports.
If you are just trying to display an image on a plane, then I think Godot should be able to show an image on plane on a HTML exported project. I do not know how Godot’s 3D abilities are with HTML, but I’ve exported some 2D projects without any issues.
If you export to HTML with debug enabled, do you get any errors on the Godot debug console and/or the web browser console?
One thing that could be causing the black screen issue is WebGL compatibility with your browser. Projects exported with OpenGL 3 require WebGL 2 compatible browsers, while OpenGL 2 projects require WebGL 1 compatible browsers.
Hopefully this helps!
(Side note: Welcome to the forums!)