Can you tell whether a tooth is a baby tooth or permanent tooth just by looking at it?

Yes. While it may take some practice and familiarity with dental anatomy, it is usually easy to tell a baby tooth from a permanent tooth. The biggest difference is the tooth's size. With few exceptions. Baby teeth typically look like smaller (1/2 size) versions of their permanent counterparts.
Yes. Most of the times, a trained dentist is able to identify a tooth as to whether it is a baby or permanent tooth just by looking at it.