How to label a image properly

[MrTTTTTwinkel]

I know we have to take the blank between one word and another into consideration while labelling a image. If there are two separated words, how do I decide when to put the two words into one label or to label the words separately. And when it comes to a whole sentence, how should I label a image with distortions, should I split the sentence into several parts and label all the parts separately into a quadrangle? Thanks a million :)