This resource uses the collection of Museums Sheffield to look at portraits and how to draw them, including facial proportions and expressions.
The My Faces interactive can be used to see how different facial features can affect expression, through shape, scale and angle. The interactive uses facial features from the portraits, which students can use to re-create the portraits or create different emotions.
You can also download a page of activity suggestions to encourage close observation of a portrait, which can be done in a gallery or classroom setting - each takes between 10 – 15 minutes (see Downloads link below).
You may also want to look at the Self Image resource from Hull's Ferens Art Gallery.