While Formaldehyde has a lot of history with embalming, a majority of synthesized Formaldehyde is actually not used for preservation. It is a precursor molecule to tons of other products, including resins, polymers, and is even found in dry cleaning solvent. So it's a good thing it was discovered!

In small doses, our livers will metabolize Formaldehyde into Formic Acid. Formic acid causes a ton of problems with mitochondria and retinal and optic-nerve toxicity. If you consume too much methanol (wood alcohol) or formaldehyde, you'll likely go blind.

In Ulyanovsk, a city in western Russia, 28-year-old Ekaterina Fedyaeva had been diagnosed with ovarian cysts and was advised that she needed a routine laparoscopic procedure to remove the cysts. During the operation, medical personnel made a tragic and irreparable mistake: instead of administering saline solution, they mistakenly gave Fedyaeva formalin, a solution that contains formaldehyde. Despite washing her abdominal cavity, Fedyaeva's organs all began to fail. On life-support machines, she told her mother "Mom, I'm dying", before losing consciousness. Unable to flush the toxins from her body, she passed away 14 hours later. All doctors and personnel associated with the operation were dismissed and Investigations are ongoing. 

Many photos contain META/EXIF data that can be used to track the pictures EXACT GPS location. 

For privacy concerns, some platforms like Facebook, scrub that META data from uploaded pictures. If you send a picture directly to someone, though, they can potentially track you down.