这两个短语的区别十分明显。took pictures是take pictures的过去式。所以took pictures只能用于一般过去时态，如：They took pictures during their stay in Beijing. 他们在逗留在北京的期间拍了照片。

take pictures是原形，可用于一般现在时态。如：I take pictures every day. 我每天都拍照片。