Look at the tutorial under how to use bot the one on announcents on the bottom of that page is a link on how to make background work.

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BLUESTACKS
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Version: 0.9.4.4078
BlueStacks is open and not minimized
Resolution: 860, 720
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AUTOIT
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Version: 3.3.12.0
Native x32
Au3 Script
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SPECS
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CPU: X64
OS: X64; WIN_81
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DESKTOP
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Aero Enabled
Depth: 32
Resolution: 1080, 1920
Refresh rate: 60
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FUNCTION CALL
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_WinAPI_GetDC: 0x04010AF1
_WinAPI_CreateCompatibleDC: 0x9C010D7E
_WinAPI_CreateCompatibleBitmap: 0xFA050CFB