The differences between object detection and image classification

Let's take another example. You are watching the movie 101 Dalmatians, and you want to know how many Dalmatians you can actually count in a given movie scene from that movie. Image Classification could, at best, tell you that there is at least one dog or one Dalmatian (depending upon which level you have trained your classifier for), but not exactly how many of them there are.

Another issue with classification-based models is that they do not tell you where the identified entity in the image is. Many times, this is very important. Say, for example, you saw your neighbor's dog playing with him (Person) and his cat. You took a snap of them and wanted to extract the image of the dog from there to search on the web for its breed or similar dogs like it. The only problem here is that searching the whole image might not work, and without identifying individual objects from the image, you have to do the cut-extract-search job manually...