This is a list of rules to check if a specific prediction can be regarded as a prophecy. 

Keep in mind that there is also a possibility of tricking people the way illusionists do today. But since most of the prophecies we are talking about are ones written hundreds of years ago, I think that case can be ignored.

 

Accurate - The prediction must be exactly as described, with no room to different interpretations. For example, one day is one day, if "one day" is later interpreted as a year, it's not accurate. 

Time bound - "The volcano will erupt" has no value if it isn't somehow time limited.   "The volcano will erupt after June 20th and before December 21st 2008" would be a way of doing this.
Without the time limitations, you can always dodge using "it still didn't happen, but it will" if something does not fit the event that was predicted. 

Specific - The event talked about must be specific.
"Great horrors" can be used to describe any event starting from the black plague to terrorist attacks. 

"The man will be punished"  can also mean almost anything. And any bad event for that person can be attributed to the prophecy.

Special - there is nothing amazing about predicting things regarding wars, politics or other common events. Media people do it all the time, and the governments pay people to be "prophets".
If you want to consider the prediction as a prophecy, it should be something that couldn't be easily known. "The DJIA will top 12000 by December 2006" is not a special enough to be called a prophecy.  "We will have an alien spaceship land on the Whitehouse lawn in 2008" is special enough.

Complete  - If the prediction is part of a collection of prophecies, you must count ALL of them, including the ones that didn't work.
Otherwise, a book I write with the two sentences: "I will win the lottery" and "I will not win the lottery" might be considered a prophecy.

 

 

Not self-fulfilling  - The prophecy cannot be a major part of it's fulfillment. 

If a man bases his son's name on a prophecy that he will have a son named George, it makes the predicament a tool of influence, but not a prophecy.

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I think that covers all the situations, but there might be other minimal requirements.

To avoid the claim that I will add more requirements to avoid recognizing a prophecy as the truth, I will give the basic rule of thumb here regarding the required rules:

If you can think of an example in which an certain untrue prediction can still pass through the filters, then another requirement is needed to remove that possibility.