it's the same as you would see on a blueprint
No, it's really not

See how all the dimensions are defined with lines parallel to the lines their measuring? You don't just throw a "9 feet" label in an extremely ambiguous location and call it a day
how did you scale it properly?
Depends on what you're using
If you're using a regular image editor, you can enable gridlines, and just count the correct number of grid lines. Or you can use free software intended for floor plans/architecture