Briefly looking at your code, I would try removing all the \$ and $$ stuff and I think it will be a good start.

Use the return( $width, $height ); and get rid of the other one. Then in the main script you test like so.

if($height > 150 )
{ # ...
}
elsif($width > 150)
{ # ... stuff here
}
# ... more stuff here
[download]

In this program you dont need any references just the regular values $var etc.

Update: You might also try scaling the images by the same percent instead of by the same numeric amount. Say its 200x100 then 150/200 is .75 so make the 100 dimension 75 (100*.75) instead of 50 (100-(200-150)) like the current code would.