I want to be able to duplicate my images inside Blender images folder (the folder that opens in blender when you want to change the image in nodes).
That way I can work faster and make a copy of my image faster.
Is it possible to do that with a script?
I tried to do it with strg+c and strg+v but it doesnt work.
Folder inside Blender:
i mean to be able to copy files when the folder is opened inside blender
One way or another, if you want to copy files with a script, you’re going to have to use that method for copying files with Python because that’s what Blender uses. The context or situation doesn’t really matter here, that’s how you copy files in Python 
If you want to hook that to an operation or a button or something in Blender, you can, but the “meat” of the function is what I shared above
In blender you can copy the image in the texture tab. I want it to make a copy not only in the texture tab, but in the Blender image folders.
Yes, I’ve told you how to do that, the post I shared is how you make a copy of an image inside of a folder. I can’t help you any more than this until we can move past this point, sorry
It causes an error
If I understand you correctly what you’re asking is whether it’s possible to customize the Blender File View that opens when you click Open on an Image Texture node. Unfortunately, I don’t think you can. People have been asking for access to the native file browser from Blender for a long time too.
Would increase your chances of solving the problem a lot if you copy/pasted the error 
Can you copy any file in any other open-file-dialog ? No ? Guess why…
It’s not a file manager… (even the File Browser window does has it in it’s name… no manager… browser…)
You only can load an image and save it again… but this is not a copy of the binary file… for example for jpeg. This would be re-coded and loose quality…
