Jane's sister Cassandra did the famous pencil and watercolor sketch of her, below, around 1810 (Jane would have been 34 or 35). It now resides in the National Portrait Gallery in London. According to Jane biographer Claire Tomalin, this sketch was regarded as "inadequate and unflattering" by those who knew her. But it is the only image we have of her that has been drawn from life. People who knew Jane described Jane as having hazel eyes, round cheeks with high color, and curly hair.
This unfinished sketch spawned every other portrait that has ever been painted of Jane.
A more flattering portrait based off of this sketch was commissioned by her family by a Mr. Andrews of Maidenhead, 1869, that is still owned by her family. (For reference, Jane died in 1817, so this was commissioned many years after her death.):
And here is a 1869 engraving, based off Mr. Andrews watercolor, used on the 1870 A Memoir of Jane Austen by her nephew Edward Austen-Leigh:
Here's one, based off the above engraving, which appeared on her biography by GE Mitton, 1905:
And then there's this one, called a "more sentimentalized Victorian version" of the above portrait:
This silhouette is owned by the National Portrait Gallery and was found in an old edition of Mansfield Park and inscribed with the words "L'aimable Jane.'"
This pencil and watercolor sketch was found in the Prince Regent's librarian, Rev. James Stanier Clarke's so called "Friendship Book," a personal album he kept of over a hundred drawings, verses, and autographs. It is speculated to possibly be of Jane from the time she was invited to view the Prince Regent's library in 1815. The book itself was sold at an estate sale to a used book dealer, and discovered in his shop in 1955. You can read a scholarly article about it here.