How can I copy an image to the Desktop Pictures folder

No, because it is located on the read-only System partition where you have no write access, even as administrator.

Instead, create a new Desktop Pictures folder in your local Pictures folder, and add the image to that location. In System Preferences > Desktop & Screen Savers panel, select Desktop, and in the sidebar, click Folders, and then [+] to add your Pictures folder > Desktop Pictures folder. Select it in the sidebar. In the array of images shown, pick the image you want for your Desktop and it is set.

You can just enter your text here. The <> tool is for code, and the additional text tool that you have used is for really long code or other long text content.

VikingOSX wrote:

No, because it is located on the read-only System partition where you have no write access, even as administrator.

FWIW, I just pasted an image into /Library/Desktop Pictures. It asks for my admin password then is added.

Yes, you are correct, though I was thinking of the /System/Library/Desktop Pictures location. Apparently, Monterey combines the images from both locations for that Desktop Pictures view in the associated preference panel.