Goncalo, as markh3565 says, it's really hard to tell. With so many varieties and varieties of varieties around, chilli identification is tricky at best. I'm no expert, but looking at your picture I'm not 100% sure that yours are Kashmiris, as they don't have the characteristic thick stem, bulbous top, gnarly, bobbly bits and thin tail.
Here's a comparison shot:

BUT.... That doesn't mean to say that they aren't, either, as there are no doubt many different varieties of Kashmiri chilli around, each with different characteristics (indeed, markh3565's Kashmiris grown from seed look a little different to the ones I grew from seed). Then there's the effect of different growing conditions, etc, etc...
If, however, the flesh is thick, and they start to turn what looks initially black in places and then a deep red on the window sill within a week, then they probably are.
The flesh of fresh ripe (fully red) Kashmiris also has a distinctive taste, which is mild and sweet.