What is a difference between "The Legend of Sleepy Hollow" story and film?

In addition to other film versions mentioned in previous answers, there is a 1980 made-for-television version that departs significantly from Washington Irving's story.  This film opens with Ichabod Crane's arrival in Sleepy Hollow on a snowy day; he is immediately humiliated by Brom Bones and his friend Frederic Dutcher, when Brom's hounds chase him up a tree, and Brom and Frederic assert that schoolteachers don't last long in Sleepy Hollow.

This film version introduces other characters not found in the story; the screenplay creates Thelma Dumkey as Katrina Van Tassel's rival for Brom Bones.  The film presents the story not as a satire of the way outsiders are not welcomed in the Dutch-American enclave of upstate New York, but rather as a lightweight romantic comedy centered on Brom and Katrina and the two people that intervene in what is presumed to be their eventual engagement and marriage.  Unlike Irving's story, Ichabod and Katrina end up together with her father's blessing, and Brom is forced into an engagement with Thelma to hide his wrongdoing in terrorizing the village in the guise of the Headless Horseman. 

There are several film versions of Washington Irving's The Legend of Sleepy Hollow.  The two most popular are the 1999 Tim Burton horror version, entitled Sleepy Hollow, and the 1949 Walt Disney animated version, Ichabod Crane or The Legend of Sleepy Hollow.  

The Washington Irving story and the Walt Disney film have the most in common.  The basic story, setting, and characters are the same.  The Walt Disney film is a shortened, concise version of the story.  It focuses mostly on Ichabod Crane at the Van Tassel party and his ride home (and subsequent encounter with the Headless Horseman).  In this film, the story begins when Ichabod Crane arrives in town (in the story, he is already living and working there when the story begins).  Ichabod's lanky figure and pronounced facial features are exaggerated in the film.  We discover less background information about Ichabod and the town of Sleepy Hollow in this version.  In the Walt Disney film, the legend says that the Headless Horseman only makes his appearance on Halloween, while this is not the case in the story.  The film also has songs about the story in it.

The horror film version by Tim Burton differs greatly from the Irving story.  The main similarities are that some of the character names are the same, much of it takes place in Sleepy Hollow, and that the Headless Horseman plays an important role.  Ichabod Crane is a constable from New York City, rather than a schoolmaster in this version.  He investigates a string of murders done by the Headless Horseman.  He discovers that Lady Van Tassel, the stepmother of Katrina, is the one controlling the spirit of the Headless Horseman (in the story, Katrina does not have a stepmother).  In the Washington Irving story, we do not know if the horseman is Brom Bones playing a trick on Ichabod or an actual ghost.

What are the similarities and differences between The Legend of Sleepy Hollow book and movie?

Washington Irving's 1819 social satire "The Legend of Sleepy Hollow" and the 1999 film Sleepy Hollow,directed by Tim Burton, have little in common.

The similarities are found primarily in the setting of Sleepy Hollow, a hamlet north of New York City. It is largely populated by Dutch Americans, and it is a mostly agrarian community. Many of the characters' names from the short story are used in the film, but the characterizations are different. Both the story and the film center on a character named Ichabod Crane who comes to Sleepy Hollow as an outsider to this Dutch American enclave, and both feature a character called the Headless Horseman, purportedly a supernatural manifestation of a Hessian soldier decapitated in the Revolutionary War.

The differences between the film and movie are many. In the story, Ichabod Crane is a Connecticut schoolteacher who comes to Sleepy Hollow, sees the bounty of its beautiful farms, and works to ingratiate himself with the prosperous Van Tassels in hope of marrying their daughter, Katrina. The village expects Katrina to marry Brom Bones, the son of another wealthy family. Brom is a bit immature—a prankster not quite ready to settle down. What ensues is a competition between Brom and Ichabod for Katrina—a competition she seems to enjoy. Ultimately, Brom uses the ruse of the Headless Horseman to scare off Ichabod, thus paving the way for him to win Katrina. Irving is making a comment on how ethnic enclaves work to preserve their insularity by ejecting outsiders—particularly the kind who come to enrich themselves.

Burton's movie casts Ichabod as a police constable from New York City sent to Sleepy Hollow to investigate a series of murders attributed to the Headless Horseman. What ensues are the makings of an American gothic horror film, not a social satire; the horseman truly is a supernatural being controlled by Mrs. Van Tassel, a witch who has pledged her soul to Satan. Mrs. Van Tassel directs a conspiracy to cover up knowledge of a will that cheated her family out of their ancestral lands and kill everyone who has knowledge of the will. Ultimately, Mrs. Van Tassel is taken to hell by the horseman, and Katrina goes with Ichabod when he returns to New York City. Brom, by the way, is killed by the horseman.

If you are referring to the movie Sleepy Hollow with Johnny Depp, the differences between that film and the book are numerous, including making the character of Ichabod Crane a police investigator rather than a schoolmaster.  That, however, is minor compared to the other differences, like turning the Headless Horseman into a serial killer from the grave, rather than just Brom Bones dressed up to scare Ichabod away from courting Katrina.

If you want a good adaptation of the book, check out the old Disney cartoon, featuring Bing Crosby as the narrator.  Despite its silliness and fun, it does stick remarkably close to Irving's original story.  I show it every year to my 7th graders after we finish reading the book!

Compare "The Legend of Sleepy Hollow" story to its movie version.

The story written by Washington Irving deals with the behaviors of a small community.  Irving shows the biased and hypocritical behaviors of all the members, particularly the school master Ichabod Crane.  He demonstrates the ability of brawn to overcome brain in the defeat of Ichabod by local strong man Brom Bones.  Bones uses Crane's intellectualism and education against him by creating a supernatural experience that Crane had read about.  Sending the fake "headless horseman" after Crane causes Crane to flee the village, much to the laughter of the townspeople.  The story isn't about the supernatural event - instead it is about assumptions and behaviors.

The movie version is about the supernatural and how the intellectual mind can overcome it.  In the movie, Ichabod is more of a scientist than a teacher.  Girls have been disappearing from town, and Ichabod is there to discover why.  He uses fancy new equipment to do so, and uncovers through his science, deduction, and bumbling good nature, that all the crimes were the result of an unruly spirit.  He vanquishes the spirit and wins the girl.  While Crane is the victim in the story, he is the hero in the movie.

The biggest similarity between the two is the portrayal of how storg supersition was in early America.  People were more likely to believe in the supernatural and to be wary of it than is true in today's America.