Presidents, just like the rest of us, sometimes become bored at work and doodle. Luckily for us author David Greenberg has assembled a collection of this work in his excellent book 'Presidential Doodles'.
George Washington was just a boy when he became bored and doodled the alternating black and white blocks at the top of a page in one of his copybooks. He then continued on down the center of the page, doodling his way through his schoolwork.
Abraham Lincoln was a serious as the photos you have seen, and seemed to not doodle, but often would leave small squiggles as above, often with the word "seal" in the middle of the squiggle. This was common at the time, and used in place of official seals.
Teddy Roosevelt often doodled, including illustrated letters to his children such as the one above for his daughter Ethel. Another example can be seen here.
Herbert Hoover was an engineer and doodled geometric patterns. Some say his doodles never included people, similar to his ideas in government, causing him to react slowly to the Great Depression. One of his doodles slipped out into the public and the patterns ended up being used on fabric in baby jumpers.
Dwight Eisenhower sketched constantly on official memos, and was quite an artist besides. This official memo does not mention troubles in Guatemala that were brewing that day, but Ike wrote out Guatemala, sketching himself as young and strong, backed up by warships.
Lyndon Johnson was a huge doodler and staff collected his work. Here we have a strange assortment of cat-devil person, a three headed woman, and violent scribbles over an image with a third leg. Third leg? You figure this one out.
Doodles of Richard Nixon tend to be dull and few in number. Perhaps he was afraid of revealing something if he doodled? This doodle was for a request from a doodle collector, and takes off on Hoover's geometrical designs, Hoover having been Nixon's friend and advisor.
What a doodler Ronald Reagan turned out to be, sketching himself a a cowboy and also football players, horses, and many love notes to Nancy. His doodles just seem to be the work of a big, lovesick kid at heart.
One final president who doodled was Ulysses S. Grant, but his doodles are nondescript, boxes and lines. In his youth however he was a talented equestrian, and watercolor painter. His art subject at the time was almost always horses.
According to the author George H. W. Bush found a loophole in the law that makes all presidential correspondence and notes public and hid his doodles away. George W. Bush and Bill Clinton failed to send samples for inclusion. George W. Bush may have been a little wary, as the closest thing to a doodle from him was the infamous "Can I Use The Bathroom" note he passed to Condoleeza Rice. A photographer caught it on film and it caused quite a media stir.