A great start is a Stanford course CS231n by Fei-Fei Li, et. al.: "Convolutional Neural Networks for Visual Recognition"
http://cs231n.stanford.edu/
It has very rich materials available for free online: notes, syllabus and of course video lectures.
If you are impatient and interested in image recognition, directly jump into Module 2: Convolutional Neural Networks.
Prerequisite would be a basic knowledge of Python.