Just curious, but is your seat high enough? Obviously I don't have enough information to tell you otherwise, but it just looks low to me even for someone with short legs.
Top tip, when sat on your saddle place the heel of your foot on the pedal (even though you should actually pedal with the ball of your foot).
Your leg should be straight when the pedal is in the 6 o'clock position.
Once you have adjusted your saddle to the correct height, your proper pedal stroke (using the ball of your foot) will leave a very slight bend in your knee at the bottom of the stroke.
This gives you the most efficient pedal stroke in terms of butt and leg muscles used, and minimises the stress on your knees.