Yes. I know. And I am not convinced that’s a good approach. 600 is pixels, and that doesn’t give convincing results on a smaller screen. Imagine an iPhone a width of 340 pixels, and you set your image size to 600 pixels… otoh, on a 1900px wide screen, a 600px image might look a bit lost.
My approach is more flexible, since it uses CSS that you can also modify to accommodate different screen sizes. And there’s only one place to modify if you change your mind, you don’t have to change all occurrences of width=600 to whatever, but only one line in a CSS file.