Niagara Herpetoculture in Ontario, Canada. He has been breeding veiled/Yemen chameleons (C. calyptratus) for about 20 years, and specializes in producing amazing individuals, especially of the translucent variety.
His photos will illustrate how to sex veiled chameleons easily, even as babies. This will apply in over 90% of all cases; there is always the odd chameleon that is a female with large spurs or a male with little ones, but by and large this method is a great way to identify a chameleon as male or female before any of the adult coloration comes in.
As adults identification should be easy; the male sports an impressive casque, has bright vertical bands of color, and has the thick tail-base typical of male chameleons where they hide their hemipenes. Females should be overall smaller, with smaller casques, typically solid green with speckles of color instead of bands, and a narrow tail base. In addition to this, males will have what are known as spurs on the back of their hind feet; a little protuberance like the spur on a cowboy's heel. Something (most) females do not have. The spur is present at the moment of hatchling, so even a newly-minted baby chameleon should be sexable this way with good certainty.