Changing the shown size of an image without changing its download size

Hello. How can I change the shown size of an image on my website (Edit page -> [Image] -> Edit -> Size -> Custom Size) WITHOUT changing the download size of that image?

On the page the custom size of the image shall appear, but when someone downloads the image, it shall be the full/original size of the image.

Thanks a lot in advance.

Hello there,

Please share the page URL where I can download your image, so I can check what the situation looks like and suggest the possible solution. If you want it to remain private, you can contact me via kharisblank@gmail.com and mention the link to this thread in your message body.

Regards,
Kharis