How do you make your own painting?

[Mackiiboy]

Hello!
I want to make my own painting to put up on a wall in my custom story. The problem is that I'm new to how models, entities and things like that works and have no idea what to do.

I can tell ya what I tried to do earlier so you understand what I want to do:
In the folder "The Dark Descent\redist\entities\ornament\paintings"
I tried to open a file called "painting_image_portrait.dds". I removed one of the images in that file and replaced it with an own image I wanted to have in the game. It worked perfectly!
The image appeared in my custom story. Then I realized that it was not a smart idea. I want to use my custom story folder and put in the right files in there, instead of replacing the regular game files.

The thing is that nothing happens when I create an entities\ornament\paintings-folder in my custom story and put in the edited "painting_image_portrait.dds"-file in there instead of replacing the main file. I will probably have to put in more files like (.mat ; .ent ; .dae ; .msh)-files before it will work.
Problem is that I have no idea how these files works, what the connection between them are and etc.

If you know an easy method to make your own painting, or know what steps that is needed to be done after you have fixed your own .dds-file, please make a comment!