From Wikipedia's page on the Voyager Golden Record:

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After NASA had received criticism over the nudity on the Pioneer plaque (line drawings of a naked man and woman), the agency chose not to allow Sagan and his colleagues to include a photograph of a nude man and woman on the record. Instead, only a silhouette of the couple was included.[13] However, the record does contain "Diagram of vertebrate evolution", by Jon Lomberg, with drawings of an anatomically correct naked male and naked female, showing external organs

After following the links to the criticism you find:

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Linda Sagan decided to make the figures nude to address the problem of the type of clothes they should wear to represent all of humanity and to make the figures more anatomically educational for extraterrestrials, but some viewed their nudity as pornographic.[15] According to astronomer Frank Drake, there were many negative reactions to the plaque because the human beings were displayed naked.[16] When images of the final design were published in American newspapers, one newspaper published the image with the man's genitalia removed and another newspaper published the image with both the man's genitalia and the woman's nipples removed.[17] In one letter to a newspaper, a person angrily wrote that they felt that the nudity of the images made the images obscene.