The upload could prompt for having the picture uploaded in three ways:
1) Full resolution @ 72dpi (huge picture but 72dpi)
2) Original Size but with higher density (thus higher dpi but preserving the original viewport dimensions)
3) Downsized, as in having the original dimensions but downgraded to 72dpi (thus preserving disk space)
Pictures are "bigger" than words... I will upload a screenshot so you can sense how this could be unpleasant for longer threads.