Gravitational lensing by a massive cluster of galaxies produces lots of streaks, arcs, and other distorted shapes. The images of distant galaxies have been transformed when their light passes through the warped space within the galaxy cluster.
Astronomers know that these distant galaxies, if seen without the intervening cluster, could look like normal galaxies. Or, these galaxies might have strange shapes due to galaxy interactions. Also, since distant galaxies are seen as they were earlier in the universe, some are still developing their shapes.
This lack of knowledge about the true shape of a galaxy that has been distorted by gravitational lensing makes interpreting their images more difficult. One way to comprehend the distortions is to run a simulation. Take a well-known galaxy, and simulate the distortions that its appearance would undergo via gravitational lensing.
That process is demonstrated in the video below. The simulation imagines the Whirlpool Galaxy passing behind the massive galaxy cluster Abell 2744. Astronomers in the Frontier Fields project have studied Abell 2744 carefully and have a detailed mass map for the cluster. Using that mass distribution, they can calculate the lensing effects for the simulation. Note that this is just a demonstration of the image distortions due to gravitational lensing. In reality, galaxies don't pass behind clusters at such superluminal speeds, the Whirlpool would appear much smaller, and many other caveats.
These demonstrations are useful in comprehending the types of image distortions one might see. The really hard task is, however, to take an observed distorted image and try to re-create the actual, undistorted image. I have seen that attempted a couple times with mixed results. Maybe I can find one of those attempts and write that up as another blog post.
For a another perspective on this video, see this Frontier Fields blog post.