@VeronicaMui its fine to use whatever you want, but use it wisely. Reference should just be exactly that. For example, If you need to know how armour connects to a body, get loads of pictures of armour and study them, then work out how your armour would connect to your character. Work out how armour reflects light, and apply the theory to your lighting setup in your artwork. If you want to steal armour designs, steal em, but steal from lots of places and put em all on one character, and change em a bit, so your character is now unique. No copying there! If you just find a picture of a knight and copy it exactly, thats not using reference properly.
Its fine to steal. Just dont get caught! π