The controversial Teen Mom star posed for the photos a few weeks ago while a friend took pictures.
"Amber fancies herself an old-fashioned pin-up girl," an insider tells RadarOnline.com exclusively.
"She posed the way she thought a pin-up would."
Wanting to leave something for the imagination, the 20-year-old strategically posed at angles that didn't expose her most private parts.
According to the source, Portwood was at a friend's home when the mood struck her to drop her clothes.
"She just wanted to pose!" the source said.
As RadarOnline.com previously reported, the mother of one inked an enormous tattoo of her two-year-old daughter, Leah, on the right side of her torso – a tattoo which is prominent in the nude photos obtained by RadarOnline.com.
"She got the tattoo as a way to show her commitment to Leah," a source told RadarOnline.com.
Naked photos are just the latest scandal to rock Portwood’s already dramatic life.
Check out what our friends at Egotastic have to say about Portwood’s nude photos and their comparison of Naked Amber vs. Clothed Amber!
Although Portwood's lifestyle is detailed on a reality-TV show, it plays out more like a soap opera; she and her baby daddy Gary Shirley's gal pal Ashley Williamson have each gone to police and filed complaints alleging harassing phone calls.
The Indiana native was also charged by the Madison County Prosecutor’s office last December with three Class D felonies – two counts of domestic battery and one count of Neglect of a Dependent – as well as one misdemeanor charge of domestic battery.