I usually get Web page designs that I have to craft HTML/CSS for.
At the moment I use tools such as OS X's own Preview to size up various parts of the designs I get in order to extract widths and heights that I can use in my CSS rules.
Is there a tool that can come handy for doing this? For example, when I draw a rectangle around a specific component in the page, I want it to also permanently show the width/height of that rectangle.
Looking forward for your suggestions.
EDIT: I found a few "ruler" apps on App Store that are very helpful but are not exactly what I am looking for (e.g. they do not annotate the image itself, but rather are on-screen tools).