Yes it is, but you'll need to connect the photoresistor in series with a plain resistor and the value of the plain resistor must be chosen so that the digital input switches between a HIGH and LOW state at the brightness you want it to. You might find it convenient to use a potentiometer here so that you can adjust the value. You would connect the digital input to the junction between the photoresistor and the plain resistor, and the free ends to 5V and ground.