When checking site speed with for example Page Speed (as the website speed seems to matter nowadays) many images don't have image sizes specified in IPB.

Should this not be implemented from the get go in the IPB?

Implementing image size in HTML is only really pertinent if your not showing the image in its native resolution

Why add extra code to tell a web browser something's size, when it's already that size to start with

Because pages render quicker that way.

I guess it would probably be faster from cache, it would maybe add a little more if you had to load the extra code but I don't think it would be much at all, I think it would probably benefit a lot on some older browsers with slow rendering speeds, but once hardware rendering comes in pages will render instantly but I still think it would be nice to implement this.

Although IPB is already a fast script, faster than wordpress but often has more data to load.