No, it's not. Dragging the icon for the image into the icon for the image viewer is exactly the same, in that you're specifying "open this file with that application". Doublie-clicking is most certainly not the same, especially when Windows defaults to "hide known file extenstions" and your malicious application is named "bigboobies.jpg.exe" with an icon that looks like a thumbnail of some boobs. The user sees "bigboobies.jpg", thoughtlessly ignores that no other legitimate images on their system show a file extension, and double clicks it; the malicious application now executes. Hell, if known extensions are hidden, simply naming it bigboobies.exe and giving it a titillating icon would fool 99% of users, even power users.
Here's why:
Typing "image_viewer.exe bigboobies.jpg" would launch image_viewer.exe, which would then tell you the file was not found. Dragging the icon of the "image" to the icon for "image_viewer.exe" or typing "image_viewer.exe bigboobies.jpg.exe", were you not to notice the ".exe" at the end, would launch image_viewer.exe, which would then complain that the file you fed it was not an image. Double-clicking an icon triggers the default action for the file type of the file the icon belongs to; in other words, if it's a sneakily-named executable, it executes it.