Batman First Appearance: Detective Comics #27 and How to Identify It

Batman first appeared in Detective Comics #27 (cover date May 1939), published by DC, by Bob Kane, Bill Finger. The source puts it this way: "The very first appearance of the Bat-Man in the six-page story".

• Cover date: the CGC census record lists the issue date as 5/39.
• Interior story content: the story also contains the first appearances of Commissioner Gordon and the revelation of the Bat-Man's secret identity as Bruce Wayne.

• Indicia: the small print on the first page or inside cover gives the issue number, date and publisher; reprints usually say so there.
• Cover price and barcode: a price or barcode format that did not exist in the year printed means a later edition.
• Paper and staples: decades-old newsprint is tan at the edges; bright white pages on an old date are a warning sign.
• Restoration: color touch, trimmed edges and married covers are common on expensive keys; a grading service can detect them.

Shoot the front cover flat, straight on, in even light, then the indicia page and the back cover. Include the top edge and staples in one frame. The app reads the title, issue number and cover and matches it against the checks above; the indicia photo settles most reprint questions.