For comic a comic book collector, authenticity is all-important. When your comic was published, and if it is a real first edition, can mean the difference between an investment and a waste of time and money. Depending on the comic book, there may have been multiple prints released. There are a number of ways that you can tell whether your comic book is a first edition or whether it is fake.
Look under the copyright information for the print edition. Some comic books will say something along the lines of "5th print," and will give the dates for all of the previous prints that came before it. Others will simply say which printing it is. If a comic book is from the first printing, however, there will rarely ever be anything that tells which printing it is.
Compare the comic book with one that you know to be real. Generally, a fake print will have small details that differ from the original. For instance, the pricing information might look slightly altered.
Research where and when the comic was originally published. If the information does not match your copy, you have a fake. Also look at the condition of the comic book. If your copy is in mint condition and looks brand-new but says it was printed over 50 years ago, it is likely that you have a fake.
Take the comic book to a professional dealer. Someone who makes a living by dealing with comic books can help you authenticate your book.