How to label images without interesting objects ?

[siemovit]

Is it possible to let some images unlabeled ? For example, if you have certain images where there is no object to label, is it possible to have the format :
1
0 0 0 0
I am not sure about how to write that being not familiar with "event". I'd like to have a default "(0 0) -> (0 0)" meaning in the text file (line 1 : 1 ; line 2 : 0 0 0 0), so that I can just click on "Next" and save the picture labeled like that because I have a lot of images without interesting objects. However, when there are objects, I'd like to cancel this "default" box, by just clicking somewhere in the picture and save the coordinates of the boxes in the text file.

Any leads on how to do that ?