1. create the ortho images
2. go to the proper ortho view
3. click the view tab
4. image plane > import image

You can also...

1. create the orthos
2. create a material (like a lambert)
3. click the checker box of the material's color
4. select file and link to the ortho image
5. create a poly plane with the correct aspect ratio
6. apply the material with the ortho image to the plane