Gravitational lenses produce different shaped images depending on the shape of the lensing body. If the lens is spherical then the image appears as an Einstein ring (in other words as a ring of light) (top); if the lens is elongated then the image is an Einstein cross (it appears split into four distinct images) (middle), and if the lens is a galaxy cluster, like Abell 2218, then arcs and arclets (banana-shaped images) of light are formed (bottom). Image credit: ESA
The third graph is interesting and points to an instance of compressed sensing. If we knew exactly the galaxy cluster between the image and the receiver (the Earth) then, with the object moving in the back and several picture taken from Earth of that object through this galaxy cluster we would have an instance of compressive sensing. Since the Hubble is the only one to take that picture, the Hubble itself would act as an instance of a single pixel camera with the DMD replaced by a whole Galaxy. I just wonder when compressed sensing will be used in the different techniques used in weak lensing. (see the review on Cluster Weak Gravitational Lensing).