A client generating HTTP traffic can have their usage classified as Text by Traffic Analysis. The type of HTTP traffic is classified by the content-type header provided in each html page. When this content-type header specifies "text/html" it will be classified as Text. Conversely if the html content-type header specified "image/jpeg" it would be classified as Images by Traffic analysis.
For more information about MIME media types see the descriptions here: http://www.iana.org/assignments/media-types/audio/index.html