Additional file-related features and issues within Microsoft Teams for business
Since I can't select a comment to "Accept Answer" I will quote them here. Both Brian McLain and Tim are correct, the band at the bottom of the page when viewing pictures cannot be resized or removed, it is there to display minis of other pictures that would be sent in the same message; why it is there when only one picture is sent or does not disappear when not selected is an oversight. The only thing to be aware of is if you are being sent 'large' or 'tall' images compared to your monitor (I think it is a scaling quirk) then the bottom will be cut off (for reference, the image I started this off with is 4000x2200 and my monitor is 1080p).
"I don't think you can reduce the space it takes or remove the display. I can't find a setting anyway.
I believe that space is reserved for image preview if multiple images are sent in the same chat line. That's what I have seen. Agree it is unnecessary and takes too much space." - Brian McLain
"I just sent a feedback report for exactly this problem. The issue is the images opens partially zoomed in, hiding the bottom part. I've already had calls where the user did not see the info on the bottom of an image because it was hiding under the band when they clicked on the image in the chat. Plus there is no use for having a big band for a gallery if only 1 image is present, and if it is there it should be much smaller or collapsible.
It should open with the full image in view initially, without a part hiding under a band because I don't expect to have to resize on opening to see it fully." - Tim