picture size - column "Hyperlink or Picture"

Hello,

I have a column of type "Hyperlink or Picture" and let it format as image.

How can I give the image a fixed size? For example, the image is 1000x500 pixels.

I want the image to appear on the form in the size of 200x50 pixels.

Have already tried something with Css, but it does not work.

Thanks!