A flawed version of the most collected Australian stamp in the world could fetch its owner up to $100,000 – barely a month after he failed to sell it on eBay for 99 cents.

It was discovered recently at a rural Scottish stamp fair, then brought to the 2013 World Stamp Expo in Melbourne where it was valued.

The Penny Red with sideways watermark.

The stamp's owner has not being revealed but it is known he tried to sell it on eBay after discovering it had a sideways watermark, suggesting it had been fed into the printer the wrong way.

The stamp is a common Australian Penny Red, of which more than one billion were printed early last century.