Image Click to Enlarge

This is uploaded by  CUT PASTE in COMPOSE mode.  

This is RIBBON INSERT FUNCTION for a photo.

SWITCH TO HTML MODE

That's hopeless.  Don't try.  One post said "download pictures in HTML mode" and they will "click to enlarge".

http://khepworth.blogspot.com/2011/04/how-to-make-picture-enlarge-when-you.html

DRAG DROP MODE

Blogger doesn't support drag drop mode.

RESULTS

When I use the RIBBON INSERT PHOTO function it will click to enlarge.

When I use the new easy Cut Paste (Ctl-V) function, the photo will not enlarge, though you can still right click and display it large in a new tab.

A QUIRK

When you Cut Paste a photo, and later return to COMPOSE mode to edit, the cut-pasted photo will only appear as a gray square.    But a photo added via the ribbon photo function will appear as a photo.   

Whichever way you originally uploaded a photo, in COMPOSE, when you click on it, you get the same edit menu.  (Left, right center, and then plus minus for size, and then a Pencil for more features.