Because their conjugation rule is different. Please take a look at this page, the part of "Two Types of Regular Japanese Verbs". http://www.epochrypha.com/japanese/materials/verbs/ 開ける: あけ doesn't change when this verb conjugates. 開けない、開けます、開ける、開ければ、開けよう 撮る: る changes when this verb conjugates into ら、り、る、れ、ろ. 撮らない、撮ります、撮る、撮れば、撮ろう I hope this helps you.

撮らないでください is correct. So we don't say 撮るしないでください。Yes, it means "don't" ～ない or ～ないでくださいis "don't"。　The part ”～” of verb conjugate.