Irfanview offers an option to capture just the active screen. I wanted to do it with this, since it offers the option to not capture the mouse cursor.
What do you think about adding the following (or something similar) to your code, Sean?
Else If aRect = 3
Loop % mC
SysGet, Mon, Monitor, %A_Index%
nL := MonLeft
nT := MonTop
nW := MonRight - MonLeft
nH := MonBottom - MonTop
If ((mPx >= nL) AND (mPx <= nW)) AND ((mPy >= nT) AND (mPy <= nH))
Then option 3 would be to capture just the active screen, ie the monitor where your mouse is currently. Such as: