The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The given source file is cropped from a Playboy centerfold.
This image is a picture of Lena Söderberg, shot by photographer Dwight Hooker, cropped from the centerfold of the November 1972 issue of Playboy magazine.
According to Hutchison, Jamie (May-June 2001). "Culture, Communication, and an Information Age Madonna" (PDF). IEEE Professional Communication Society Newsletter 45 (3). (page 5 second column second paragraph), this image is distributable but not free.
Moreover, Lenna photo has been pointed to as an example of sexism in the sciences, reinforcing gender stereotypes.
Please use well known and free test images.
Please also submit the md5sum, sha1sum, and sha256 of this file as a bug report for Lintian.