I noticed the following mold in a corner of my garage. Where is it coming from, air flowing around the door or hinge? Could the garage door (right), contribute to this? How does one stop this from happening?

At this time, my plan is to cut out the sections that have mold and replace them with mold resistant drywall that I have on hand.

Here is a pic of the outside.

I'm on the East coast in Canada (ie. Maritimes). This issue has appeared a while back, just getting to it now. It doesn't seem to have expanded.

We use the garage a few times a day as the car is always parked in it. The ride-on lawn mower and snow blower are typically parked near the corner for easy usage which might bring in excess moisture to the corner?

Update 2

I had the chance to open up the walls. It seems superficial. Noting the black strips along the edges look to be some sort of caulking.

Back of the drywall shows some traces of mold.

Maybe all I need to to put a mold resistant drywall patch, which I conveniently have sitting in the garage?

I wonder if the line on the moulding isn't due to air circulating via the hinge?

Update 3

I should have posted these earlier. A closeup of the hinge and both front and back of moulding. At this point, this seems to be surface only?

The green drywall is the new patches that I cut and haven't installed yet. They're from an old piece cut out from left overs used in the bathroom a while back at another house.