Well, actually, this function really should have been a private method (of the image object). But I guess it got mised. PHP 4 did not allow for private methods so none existed when we did still support PHP 4. Perhaps not all that should be private got discovered when we changed for PHP 5 and marked methods private.

At any case, the documentation will generally tell you the use of a function. In this case no such documentation would be an indication that the function is not inteneded for general use.