Question: When I drag and drop image files from Windows Explorer to Excel,
nothing happens. 
Can you make it work? 

I’m particularly interested in jpg/png or ico files,
but I’d like to be able to do it with all image types.

I have been inserting them using Excel’s insert image features,
but it doesn't seem to be super productive. 
I was looking for a faster, efficient option to improve productivity.

Answer: 
Here is a workaround: drag into MS Word and then drag into Excel. 

Definitely better then going through the Insert system.
The easiest way I've found is to copy the image itself by viewing it first and then copy it into the clipboard. Then it can be pasted into Excel.