From you picture I cant see the breadboard clearly enough to see if you have it connected correctly.
But if you have a 3v supply you should be able to test it without the pi.
So connect 3v+ to one end of the resistor and the other end to pin 1 on the 4N26.
Now connect pin 2 on the 4N26 to ground ( ground being the other side of your power supply.)
now connect pin 5 on the 4N26 to the 3v+ on the power supply , with the meter set to volts connect the red lead to pin 4 on the 4N26 and the black lead to ground.
your meter should read 3v , if you disconnect the 3v from the resistor your meter should red 0V
So here's an example
red lead on right is connected to 3v psu and pin 5 on the chip , meter is connected to pin 4 on the chip and ground on psu
resistor is connected to pin 1 on the chip and pin 2 on the chip is connected to ground , no 3v on the resistor so meter reads 0V
now you can see I have connected 3v to the resistor and now the meter reads 3v.
and here is a close up of the chip and connections