The photo of Shug that Celie sees early in the novel demonstrate some of Shug's superficial traits, most of which are reflections of her deeper character. Celie's response to the photo is significant as well.
In the image, Shug seems to be confident and strong but also seems to have been through quite a bit in her life. She dresses flamboyantly and clearly does not attempt to conform to social conventions. This is Celie's interpretation.
Her emotional response is one of immediate admiration and even adoration. The romantic feelings between the two women develop later, but even at this early stage Celie is taken by Shug's image.
Also, at this point, the person Celie sees in the picture represents a stark contrast to Celie's view of herself. Shug is assertive and bold. Celie is meek and submissive.