Stephanie,
Images taken with devices like phones store metadata about the image taken. They can contain lots of information like the GPS location and the images orientation. Here is a post I wrote about running into this problem.
Proper Image Rotation from Mobile Uploads
This is not a bug. It is intentional. When a device takes an image, they want to be immediately ready to take the next image. If the device has to spend resources reorienting the image, it slows the whole process down. Instead it just stores the information.
I hope this helps!
Regards,
Tom