So based on what you set in the Attachment Options --> Maximum Attachment Image Dimensions sets how these are re-sized on upload.
It's not clear from the explanation text that images will actually get re-sized (I did see again that Brogan has the information in his FAQ). I've been allowing members to upload HUGE images because I didn't know XF was able to re-size them.
Would it be possible to make it more clear from the explanation text that re-sizing will happen server side if the dimensions are breached?
"The maximum allowed dimensions for attached images (width x height). Use 0 or blank to not restrict dimensions."
"The maximum allowed dimensions for attached images (width x height). Use 0 or blank to not restrict dimensions. Images greater than (width x height) are automatically re-sized down" (or something along those lines)