The types of picture doesn’t really matter.  They can all be different sizes and color.  I have used black and white with color pictures, as well as a few sepia tone photos.  They can be portrait pictures or landscape ones.  Just find photos you like.  After all,  it must be a pretty nice and warm memory  for you to have a photo of it.  I try to keep a balance to my photos.  In other words I try not to have an odd number of photos that are color or black and white.  There is always a place on your quilt where you can place 2 sepia tone photos and have it look balanced.  But not quite so easy when you have 3 to place.