There is something called EXIF data which is embedded in digital images. One bit of that data tells computers what in orientation the photo was taken. Some cameras\phones don't do this properly or the data gets messed up and interpreted incorrectly - Older iPhones are notorious for this. You can have the same image and it will display in different orientations in different programs. You can of course just manually rotate an image in any photo program to get what you want..
http://keyj.emphy.de/exif-orientation-rant/Your image, as I download it, has no exif data aside from image dimensions. Maybe uploading them to the forum strips them of exif data... If does resize them so it could be in that process it removes the orientation flag too.
Yes the site removes the EXIF data - it should preserve the orientation but not in your case!