Australia releases many variations of stamps. Typically stamps released in miniature sheets seem to be on gum paper, while others are on self-adhesive paper. The perforation of these stamps is an easy way to recognize them.
- Gum stamps usually have finer perforation (14) while self-adhesive stamps have more spread-out wavy perforation (11 or 11½).
- Check the corners of the stamps. Gum stamps have regular corner perforation while self-adhesive stamps have a more rounded corner with missing perforation in the corner.
- Gum stamps also have pulled effect to perforations, while self-adhesive stamps have neater separation.
I have noticed the above differences only in Australian stamps. My guess is these might be similar for other countries too like USA, Great Britain etc.