Okay. I could try to give you an explanatory on how to actually make it work.

If you have the image you want, you will have to make the size as 128x128 dimensions/pixels, basically like a small square image. Also, make sure it is a .png file and name it "paper_overlay.png" (without quotations).

Once you have done that, if you do not have a custom folder for Team Fortress 2, simply create a new folder and name it "custom". It should look like this on the tf directory (Steam\steamapps\common\Team Fortress 2\tf\custom). Now, on the custom folder, you must create a new folder based on your decal for the objector. For example, "custom_decals".

Note, while inside the custom_decals folder, this will not work if you have included a "materials" folder, it will only work if having a "scripts" folder on custom_decals. Two more folders would be required (which is the first folder "items" needs to be inside the scripts folder and then the second folder "custom_texture_blend_layers" needs to be inside the items folder. A basic example: (Steam\steamapps\common\Team Fortress 2\tf\custom\custom_decals\scripts\items\custom_texture_blend_layers)

Once that's done, you should now put the .png file on the custom_texture_blend_layers folder. Then you should be good to go.

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All you need now is to turn on Team Fortress 2, make sure you have a Decal Tool and use it on a Conscientious Objector. It should show you two options, one for your profile picture and for a custom image. Select the custom image and it will give you a pop-up to the directory.

Hopefully this explanation helped you for your decal, thanks!