That's a good question. It would be helpful to know what game it is and what region it was released. The best way to tell is by comparing a like original. There are a plethora of shrink wrap machines out there that come in all shapes and sizes. In another life I worked at several different Kinko's locations and they each had a different brand and style shrink wrap machine.
Now I'm not saying that your game isn't originally sealed because there are still plenty of factory sealed games in circulation. Sometimes, there are certain tell tales with specific publishers.
Check out this video from
Jim Leonard about PC games and OE shrink wrap and non original. Hope it helps!