On some devices (such as the Samsung ones), captured images in portrait mode are rotated 90 degrees; and on other devices (such as the Nexus devices), things seem to be just fine. You won't notice this if you have a look at the file using the Astro app, for example, but you will if you see the preview in the Facebook share dialog.
This is a well-known challenge for many Android developers. Images may contain metadata about the rotation degree, but apparently not every app respects that metadata. What is the best solution? Should you rotate the image every time you want to display it? Should you rotate the bitmap itself, which could be very time and processor consuming?