How Can You Tell If It's Uncirc, Cameo Or Proof?

Comparison between a regular uncirculated cent and a proof cent:


An example of a cameo proof: (Notice lincoln is blast white while the rest of the coin has a reflective surface)

On the top picture, you can really see the quality by looking at Lincoln's hair in the proof vs the business strike. Beautiful!

Not all proofs have polished fields and cameo details, although that is almost 100% the case, with modern coins of all countries, which are made for collectors, sometimes in their hundreds of thousands.
Laser etching is commonly used to produce the cameo effect, although acid etching and sandblasting have been used in the past. In any of these processes some of the original detail is lost, even if it is very slight.

18th century proofs were quite often never intended to be sold to collectors, but were retained by the Mint for quality control and record purposes. It was common for fewer than 10 of them to be produced.
These sorts of proofs are very rare, and are sometimes difficult to distinguish from pristine condition coins that were to be issued for circulation.
They were first strike coins from fresh dies and struck using selected blanks. No attempt was made to polish the dies or blanks. There was also no attempt to cameo finish the details, which would have been very slightly degraded in the process.