The patch is small, about a fingernail in size.
Elsewhere on the packet they used two colors of ink: a very dark blue (this) and a lighter blue. I expected it to be some kind of alignment pattern, but only one of the inks seems to have been used here, so that's not it...
What is it for, why would they bother printing it? An ink+paper resolution/absorption test?
Can you provide some more context?
There's a description under the image. Starts with "the patch is small". I'm not sure if it's visible, because others are commenting as if they haven't seen it...
I'm not sure what else to add. Small paper packet of medicine, printed using two ink colors, only one used for this pattern. This is on one of the small underflaps at the end of the box.