Allows to crop the display of an inserted picture. Only the display gets cropped, the inserted picture is not changed. A picture must be selected to enable cropping.
In Impress and Draw no dialogue is shown when you click the icon, but you see eight cropping handles. Open the context menu of a selected picture and choose Crop Picture, if you want to use the dialogue for cropping.
Drag any of the eight cropping handles to crop the picture.