bbcode - "[img]" tag formatting for x% simple visualization code and full link to directly load in 1:1 scale -

i want know simple complement code [img] shown @ x% of original size. thinking [img width="50%" height="50%"] doesn't make sense. instead of huge code, place in brackets show image @ x% scale? php code?

and other question. i've seen little "tag" place in direct link load image full resolution or lower size. tried find on web, don't know how describe being specific in search criteria. example, pasted http://example.com/image.jpg=fullscreen , image load on entire screen instead of clicking on zoom in. or http://example.com/image.jpg=half show in half resolution.