When doing a character sketch, it is probably bet NOT to include a picture of the character. By including one, you have robbed your reader of the opportunity to create his own image of the character. That is one of the great things about reading.
When they have only the words of the author to guide them, readers have the ability to bring characters to life within their own imaginations. It gives readers the feeling that they know this character personally.
It is always fun to see your favorite fictional characters come to life on the big screen, but then again, it also takes away that feeling of familiarity that a reader has developed with a character. Whereas before you felt like a close friend of the character sharing a secret, the movie makes you feel like a voyeur, a peeping Tom listening in on a private conversation.
I would not include a picture. As the above posters have noted, the things you say with words are supposed to help the reader form a mental picture of your character. Think of a book you have read and loved. You probably have pictures in your head of the characters. If you see a movie of the book before you read it, do you still form your own images? Or are the actors from the movie who you see while reading?
I loved the book Gone With the Wind, but unfortunately I saw the movie first. Scarlett O'Hara was Vivien Leigh in my head, even though one of the first passages of the book said that Scarlett was not beautiful.
I don't see a problem with attaching a picture after you develop the sketch. As speamerfam says, the purpose of a character sketch is to write a description of a character. Think of it as taking the most important things that a reader should know about the character and then putting those things into a nutshell.
This type of writing assignment lends itself particularly well to a word web graphic organizer. Write the name of the character and circle it, then draw spokes all around the circle. On each spoke, list a characteristic that the reader should know about the character. You can go even further and draw a small circle around each characteristic, and then draw spokes from the small circles. This organizer will help you develop details for your character sketch.
After you have drafted your sketch, read through it and ask yourself for each sentence, "Does this sentence support my purpose of showing the reader important things to know about the character?" Revise and edit for content relevance, then reread and edit for spelling, punctuation, and grammar.
Generally, it is probably best not to include a picture. If you are assigned to write a character sketch, you are expected to "sketch" a picture with your words! When you are describing a person and his or her character, the idea is to help the reader "see" the person you are discussing. Often, a person's character and appearance go hand in hand. Have you ever thought about how sometimes a person looks just as you would expect him or her to look, based on your assessment of the person's personality? When you are writing a character sketch, a description of the person might be important, too, for that reason. A miserable person might have many frown lines and dress in dark colors. Someone who is the life of the party might have a different kind of face and attire. Consider painting a word picture of the person as you describe character.
Another aspect of character development in a paper like this is action. What we do reveals our character, doesn't it? What does your subject do? Does he or she sit quietly or bounce around? Does this person like to read and play the piano or work out with weights? Or both?
A character sketch that tells the reader what the subject looks like and what the subject does can be quite revealing, even without a picture!
Good luck to you.
A character sketch mus rely on words only. A picture can be an additional input, but it should not become a substitute for what mus be included in the verbal sketch.
When a picture is included, care should be taken to select a picture that is in line with the written description of the person.