Copy/paste your text below to know where are letters O and digits 0.
In their written form, the letter O and the digit 0 look alike. Usually it is not a problem because with the context, we understand which is which.
However, when the text has no sense in itself (for example an identifier or a password) and we have to dictate it to someone or to pass it from one screen to another support (paper, phone,...), it becomes critical to understand which character is a letter O and which is a digit 0.