Let's start with a pair of 19th century albumen photographs taken of Ramses I, which I purchased on eBay. This mummy was stolen by grave robbers and brought to North America around 1860. It ended up in in the Niagara Museum and Daredevil Hall of Fame in Niagara Falls, Ontario for 130 years before going to the Michael C. Carlos Museum at Emory University in Atlanta, Georgia, then in 2003, back to Egypt at the Luxor Museum. These photographs seem to have been made very near the time of discovery, since the mummy looks "fresh" and undisturbed. [click on image to enlarge]
When you compare these to a more contemporary image likely made at the Niagara Museum, there is certainly evidence that the body had been repaired or "retouched", to say the least.
In Chile and Peru and along the Andes, are found mummies of usually sacrificial offerings, often children, nestled high on mountaintops or in dry caves. Wrapped in fabrics, they are naturally dessicated and preserved with astounding naturalness. While the Egyptian mummies were eviscerated and embalmed in a warm climate, the Andean mummies were simply placed in a rocky cave to protect them from scavengers. The cold, arid mountaintop did the rest. The 15-year old "Llullaillaco Maiden" was sacrificed more than 500 years ago along with two other children on top of Mt. Llullaillaco in northern Argentina, at 22,000 feet.
The Chachapoya mummies of Peru were found in caves and are also over 500 years old (above, right).
Northwestern Europe, the British Isles and Ireland are known for their extensive peat bogs. When peat was being harvested, many cadavers and artifacts were found deep within the layers of old peat. Organic material was especially well preserved, one could say pickled. Leather, fabric, wood, animals, and people were unearthed and placed in collections throughout the region. An extensive and wonderful website about the bog people can be found HERE.
In many cases there is evidence of human sacrifice or simply murder.
There are many examples of deliberate human preservation, such as the extensive embalming and restoration performed on Vladimir Ilyich Lenin and Evita Peron. However, few are as grotesque as the preservation of Julia Pastrana (b. 1834), a Mexican First Nations circus performer with hypertrichosis. Theodor Lent managed her and eventually married her. During a tour in Moscow in 1860, Pastrana gave birth to a baby with features similar to her own. The child survived only two days, and Pastrana died of post-birth complications five days later. Lent then had his wife and son mummified and displayed them in a glass cabinet. A detailed essay on her life and horrific after-life can be found at The Human Marvels.