Usually you store the text anyway, so you can select and search it, or have it read by accessibility tools. And most of the time, the letter spacing is the def

Usually you store the text anyway, so you can select and search it, or have it read by accessibility tools. And most of the time, the letter spacing is the default given by the font, so you just have to encode the position of the beginning of a run of text. So it is pretty space efficient, too.