My mother is annoying me . . . .?

i have on my cellphone a couple of pictures of some of the vocaloid, mostly miku hatsune and some anime characters i have watched. The problem is this; my mother thinks it is too lewd for me. She tells me that i shouldn't 'study' girls until i am married. She asked me to delete all the pictures. But i think she is reading too much into this. I only got the pictures because i was impressed with the artwork and took a long time to find these in good quality. What do i say to her so that i can keep all or most of them?