With Windows, if SketchUp is set either to ‘Always Run as Administrator’ or you have chosen to ‘Run as Administrator’, then drag-n-drop will no longer work.
This is because Windows prevents a ‘lesser app’ affecting a ‘higher app,’ and Windows Explorer always runs as ‘lower app’… so you need SketchUp to be set at the same ‘level’…
If you install SketchUp from its installer exe using “Run as Administrator” [right-click > context-menu], then there should subsequently be no need to change how SketchUp runs etc - and all should be well…
So then you can drag-n-drop images [and several other other file types] directly into the SKP window…