Are your pictures rotating?
I never had this problem when I was using Photoshop to process my pictures from when I joined the forums up until mid last year.
All of my 3700 pics (plus the 2000 odd ones that were lost) up loaded to these forums have been, cropped, level corrected, some have been colour corrected and all have been scaled (usually to 800x600), and exported as 50% compressed JPGs.
When I started using GIMP to process my shots suddenly many of them appeared as rotated even though I rotated them while processing. Eventually I worked out that GIMP exported images with the original image EXIF data (which included original image rotation) unless this was explicitly unchecked in the list of save checkboxes.
AS soon as I started doing this the problem went away.
I suspect this is happening to many member's uploaded photos. I know many people don't do any processing but for those that do this might be worth a try.