Falsification can be a profitable activity, but most jurisdictions consider it a crime called forgery.
Many objects can be falsified. Copies of art objects, such as paintings, have been circulated as though they were the original. Photographs have been modified to suggest something that was not actually in front of the camera. Money has had a long history of falsification. Expensive watches and gemstones also get falsified. Official documents are routinely falsified.
Entire fields of expertise have grown around the problem of ascertaining that something is indeed authentic.
See also: false document
"Photography in the Age of Falsification" by Kenneth BrowerExternal link