Right click on what? If I right-click on a jpeg in a folder or on my Desktop, I get an Open or Open with... choice, but not Import.
Where are you seeing an Import command?
Otherwise, whether I drag and drop or open by right clicking, there is not difference.
I'm just talking about in general...
You download a photo, it drops at the bottom of your browser..you right click it and open it in preview and then right click that and tell it to import into Photoshop.. now you take that same photo and just drag it into Photoshop from the folder or wherever you downloaded it, the size of the image is different.
I'll need some more information. Mac or PC? Operating system version, the browser/version you are using. Preview sounds very much like a Mac application.
So when I think I have enough, I'll try and duplicate this.
In fact if you will post a screenshot of this Preview and show the Import command, I'll have a clear picture.