Hi Bob.
No, the point I am making is that although the checkered section supposedly represents an empty section, in fact, it appears to be impossible to get rid of it. In other words, I wanted to slide something right up close to the part I cropped, but it proved impossible because the supposedly empty section continued to be in the way. Only if I use the rectangle select in Tools can I crop something without this problem, in which case - of course - it is square but if I want to put a sloping shape, the checkered section immediately seems to be activated and I have found no way to get rid of it except that it changes white but still forms the part of the pic which I wanted to cut out!
I cannot find any search facility on this forum but somebody must have asked this question before!!
Anyway, thanks for your comment.