I is quite easy to cull your photos in dt. Once the images are imported, in lighttable mode, my method is to use control, shift and F this turns on focus peaking. You will notice blue and green areas which correspond sharper images to the photo. If I want a closer look highlight the image and Control and W gets a full screen view. Deleting photos can be accomplished by using the delete key then tab and enter, this should move them to your system trash. The short cuts are for for 3.2.1 and may differ in older versions.