For the Silverlight viewer, you (as the synth author) can open the synth editor, go to the [Advanced] tab, and select 'Photo Up' and click [Save]. This way, everyone will see your photos at the same angle that you uploaded them. If you uploaded them right side up (as you have), then that's what people will see. If you uploaded the photos on their side, though, then that is what people will see, if you select 'Photo Up'.
If you have a good clean point cloud, you can actually upload photos that were taken at or rotated to funny angles before you synthed and they will actually be displayed correctly within the synth. See the second photo (2nd in 2D view - I've actually linked you to start on it) in this synth for a small example: http://bit.ly/marksvisitsynth