iFlags
The flags are in four groups that define treatment of the source, treatment of the destination, the operation to use when combining the data, treatment of the resulting image, and the color plan for destination, source and result image. The flags apply only to the defined rectangles (not necessarily the whole bitmap). You can use a bitwise OR ( | ) to specify one flag from each group. In high-level languages such as Visual Basic, you can use a plus (+) operator to specify more than one flag.
For a simple paste, use CB_OP_ADD and CB_DST_0 as the flags.
Refer to Flags for the CombineExt Method for the list of flags.