What LED are you using at the moment?
To be honest, I don't know 
I just bought a few IR LEDs from my local electronics shop (I didn't ask them for anything specific, just IR LEDs). That's why I want to know what I should be looking for. Is there any "power" value?
Did you remember to set the pinMode to OUTPUT (I have to ask, because I can't see you code)
Yes, I did. I don't have the sketch here with me (currently at the office) but it does work, in the sense that it triggers the camera.