Do these pads look contaminated?
I agree with @Daniel R Hicks.  Those pads aren't terrible, but they're obviously not new either.  New pads are cheap, so go ahead and throw a new pair on and see if it helps.

It's also possible that the pads are worn enough that even when you pull the lever in all the way they fail to make good contact with the rotor.  Are they mechanical brakes?  That problem is especially common with mechanical brakes.

Lastly, is it possible that you got some sort of oil/fluid on your rotors?  That can severely lessen braking power, and it can happen with an invisibly thin film of oil.  If you think that is the case, clean the rotors with a non-detergent solvent like goo-gone.

Also, can you describe what you mean by "shuddering"?