it is the merger of Mills & Boon and Harlequin that played a crucial role in awarding romance fiction the appearance of commodity literature, an appearance that has shaped American romance publishing at large. In other words, the genre's reputation as a highly constrained form of storytelling owes a great deal to a series of events in which the covers (and material body) of the novels were shaped by both Mills & Boon and Harlequin over the course of the twentieth century so as to promote a branded version of prose love narrative. (241)
Avon Books' paperback printing of Kathleen Woodiwiss's The Flame and the Flower (1972) and Rosemary Rogers's Sweet Savage Love (1974) [...] spawned a trend in terms of both plot and packaging but key traits of the former (sexual violence and purple prose) became indelibly linked to the latter, making the covers a sign for reactionary gender politics and soft-core pornography. (257)
The article continues its analysis into the twenty-first century, describing a variety of different types of covers/poses.