Baby's can start recognizing objects as early as 2 months, they start with identifying their mother, father, grandparents and others. They can see colors from 3 months on, thats when we should show lot of colorful rattles which lets out various sounds, here they recognize both color and sound.
We even can start reading books and show them pictures.By 6 months they can almost see and understand shapes,colours and sizes. You can show various pictures of birds,animals,house hold things, parts of body,etc. This sharpens baby's observation. I started showing various pictures to my daughter right from 6 months, she is a year and 4 months old now and can recognize everything in the house. She can point rightly to what ever we ask. Initially you cant expect any response from your baby, you ll feel as if its going to dumb ears, but believe me they are gathering all the knowledge in their tiny brains.This is what they do these days at a playschool.