I raised a ticket to SAP, and got their answer.
Following the steps below, I was able to solve my problem.
1. Download FreeImage from
http://downloads.sourceforge.net/freeimage/FreeImage3170Win32Win64.zip
2. Extract the zip file and find FreeImage.dll
3. Put FreeImage.dll into the same folder as SAPBusinessOne.exe
4. restart SAP Business One.
FYI, after I put the DLL into the same folder as SAPBusinessOne.exe,
"Integrated Camera TWAIN" is shown on the path of "Current Scanner" on "Path" tab of "General Settings" window.
This "Integrated Camera TWAIN" seems related to the built-in camera driver of Lenovo PC(My PC is Lenovo X230).
Thanks