Quality fabric just has the right feel. The cotton is soft and hangs correctly. The grain is even on the bolt - not angling in one direction. As the previous poster said, the dye is good.
Pictures do not tell if it is quality fabric you can tell just by the feel.
Do a test for your self. Go to a cheap fabric place touch feel and observe the fabric. Then go into a high quality LQS and touch feel and observe the fabric, you will see what I mean.
Its all in the feel.