MatriX, here is a slightly updated version. I added a little error checking and changed the box colors to remind you which button to use for the corners. I wasn't able to recreate the problem with the zoom. could you post a screen shot if it happens again?
sync on
set display mode 1024, 768, 32
load image "your picture here", 1,1
paste image 1, 100,100
x1=100
y1=100
x2=132
y2=132
do
cls
paste image 1, 100,100
if mouseclick() =1 then x1=mousex():y1=mousey()
if mouseclick() =2 then x2=mousex():y2=mousey()
if x2<x1 then x2=x1+1
if y2<y1 then y2=y1+1
s$=str$(x1-100)+", "+str$(y1-100)+" to "+str$(x2-100)+", "+str$(y2-100)
text 5,5, s$
if x2>x1 and y2>y1
get image 2, x1, y1, x2, y2,1
sprite 1, x2+50, 100, 2
scale sprite 1,400,
endif
ink rgb(255,255,0),0
line x1,y1,x1,y2
line x2,y1,x1,y1
ink rgb(0,255,255),0
line x1,y2,x2,y2
line x2,y2,x2,y1
sync
loop
