Color picker on imported images

Is there any way to use the color picker on an imported image to create swatches in your palette? I’ve tried several times with all the many different options they have for importing images (import as vector image, import as bitmap image, etc) and I’m just never successful. The image imports just fine, I just can’t use the color picker on it. Any help or suggestions?

Click and drag the dropper to the desired colour and release.

One can select any colour from the screen, imported images,
the Interface, or any other open application.

As far as I can tell you have to have a keyframe selected.