why some people use relative dirs using a dot, or dot and slash and others not?

Question

This is maybe a kind of dumb question but I never knew why there are 3 ways to write the same.

For instance, show an image called photo1.jpg inside the img dir:

index.html

<img src="images/img_1.jpg" alt="photo 1" />
<img src="/images/img_1.jpg" alt="photo 1" />
<img src="./images/img_1.jpg" alt="photo 1" />

Those 3 work but is one better than the other? why?

Edit, as some pointed out, the second one is an absolute path.

In that case what I want to know is what differences are between 1 or 3. Or they are interchangeable?

Answer 1

As far as I know, the second one is not a relative path, images should be in the root folder.

The first and the third one are the same, dot represents current folder.