15c Oliver Wendell Holmes Jr. Stamp (1968): How to Identify It

• Subject: known as the 'Great Dissenter,' who insisted that laws be viewed in light of a changing society rather than as old formulas to be adhered to.
• Color: magenta.

The same design was issued in more than one form. Which one you have changes the catalog listing:

• Precancel (Scott 1288a): Carries printed cancellation bars applied before mailing.
• Booklet single (Scott 1288b, 1978): A single stamp removed from a booklet pane, issued a decade after the original sheet stamp.
• Coil, vertical perf 10 (Scott 1305E, 1978): A coil version issued ten years after the sheet stamp, perforated vertically at gauge 10.
• Imperf error and imperf-between error (Scott 1305EG / 1305EH): Missing perforations entirely, or missing perforations only between two stamps, on the coil issue.

• Measure the perforations with a gauge; the same design often exists in two or three gauges, and that is usually what separates the common one from the scarce one.
• Sheet, coil or booklet: coils have two straight edges on opposite sides; booklet panes have one or two straight edges from the pane edge.
• Tagging: hold it under a longwave UV lamp; tagged and untagged printings of the same design are listed separately.
• Condition (centering, gum, cancel) is a separate question from identification.

Lay the stamp flat on a dark background in daylight, fill the frame, and keep the phone parallel so the perforations are not distorted. Photograph the back too if there is a watermark or gum question. The app reads the design and denomination; the perforation and tagging checks above settle which listing it is.