If photos are uploading sideways in Pet Picture Gallery then this means that the image really is sideways.
You are most likely looking at them using a program that is automatically rotating the image for viewing (but not actually saving the image in the rotated state). You need to make sure your images are saved in the correct orientation before uploading them.
To do this you can use any image editing software to rotate them correctly. GIMP is an excellent choice and works on all platforms (OSX, Windows, etc.). PicMonkey is also a good choice for photo editing.
If you don't want to be that advanced you can try any native tool that comes with your OS, such as Microsoft Paint or Mac's Preview.