This usually occurs when selecting images holding the control key and
the mouse button is released while dragging. To select images in consecutive
order use the shift key select the first and last image to highlight all
images in between release the mouse button then right click the highlighted
image(s) choose delete. To select images that are not in consecutive order
use the control key then after highlighting the images you wish to delete
release the mouse button then right click the highlighted image(s) choose
delete.