Beyond the racism in the image that’s quite obvious to crazy people, the other question is whether there are any real substantive comparisons between Obama and the Joker. On the surface, they don’t seem at all alike. The Joker is psychotic, and I’ve heard Obama called a lot of things — arrogant, incompetent, deceitful, a Communist — but not psychotic. Obama doesn’t seem like he’s out to kill anyone — not even terrorists — and only leaves the option of killing people on the table to help make ends meet in his health care plan.
Also, the Joker seemed chaotic but was very careful in his planning, while the chaos from the Obama administration seems much more explainable by pure incompetence.
Furthermore, the Joker was actually somewhat subtle in how he tried to destroy Gotham by psychologically breaking down the will of its people, but Obama’s methods for destroying everything are a bit more ham-fisted, such as proposing expensive new programs while we’re already hugely in debt. Finally, the Joker has always been depicted with normal-sized ears.