Hm, @Eyal I do wonder if it’d be possible with current forms. I don’t think so as a true 'side by side" with the normal dialog box, in one sense because the forms are set to stay in the center of a window and expand on both sides equally, and that’s hard-coded into the software.
I think the image viewing could potentially work, in that it is already possible to embed the attachment viewer into a form natively, unlike Geomap. (Though it would be nice if Geomap could be embedded natively into forms).
It might be possible to force the form to be extremely wide and have a conditional definition based on the presence or absence of a null value in the attachmentID field, and then have one conditional form definition include a gigantic panel on one half of the form where the attachment plugin would display. I’ve not experimented with pushing the form definitions in that way.
I think it would be hard to set something up that would work consistently on different monitor resolutions in the current form system.