If you are describing the contents use present tense. "The figure looks so skinny." If you are describing the style use past tense. "The artist has painted a skinny figure in the foreground." The contents are as you see them now. (present) The style is how the artist painted it. (past)

Use the present tence. Sometimes people will use the past tence like this: 'The artist has painted him thin and skinny' This is also acceptable, but it is better to use the present tence, 'In the picture, he is skinny'. I hope this helps, David.