I’ve tried searching this on YouTube to no avail.
Basically I want to make a postcard like this:
…using a “normal” postcard and some tool.
I’ve initially thought about a standard hole puncher, but it only makes 1 hole at a time (there are 80 holes in the postcard above), and thus requires a lot of time overall because correct positioning relative to the other holes needs to be achieved somehow.
Is there a better method?
You can buy special pattern producing scissors for it.
I bought this set from Fiskar that has a scissor pattern for the kind of perforation we’re looking for - 5th pattern down, 
@elanlei @LC-Canada Wow, that was quick! Much appreciated for the hints, that’s what I was looking for 
You’re welcome - I’ll be curious if others have other cool tools or methods to share!
My problem with that would be cutting in a straight line. 
I can’t cut a 90 degree angle if my life depended upon it. 
I like @LC-Canada’s pinking shear suggestion! 
And I love your idea for a do-it-yourself postage stamp-shaped postcard. I’m sure some of the “teeth” on the perforated edges would be bent or torn along their postal journey…but that’s just part of the process, right? Please share your results!
There are also dies like this:
I would strongly recommend shaped scissors over a cutting die if the only goal is to cut the edges of a card into a postage stamp or other edged shape. Although @S_Tuulia is I think right that in principle you could use a cutting die without an embossing machine (used with cutting dies), in my experience the pressure an embossing machine exerts onto the paper/die is far more than the average person can accomplish, and I think scissors would give a cleaner and more reliable result.
(full disclosure: I did try using cutting dies someone gave me this way (knife, roller, really heavy slab of marble gone over with the roller…) before I got my embossing machine, and the results were…non-optimal. But maybe others have had better results than I did!)
My mom had pinking shears she used for sewing projects sometimes. They come in various designs and would give you this effect just by trimming the sides of the card. 
Now I had to try how hard I press and, not very hard, and actually not press, but how I’d peel a carrot, dragging.
But, scissors might be easier to get. My problem with scissors is, if I try to fix the edges, it doesn’t always cut perfect, or straight (not the fault of the scissors).
Here’s my little bird from a die, made using a knife. The ones with only lines (no holes like in this) are much easier but this isn’t hard either.
Bad side with a die is, you can’t change the size.
Wow, you have an nice touch. I could never get such results with a knife and a die. My embossing machine saved me!
