BCGControlBar Pro for MFC
BOOL CBCGPDialog::SetBackgroundImage ( UINT  uiBmpResId,
BackgroundLocation  location = BACKGR_TILE,
BOOL  bRepaint = TRUE,

Sets the dialog box's background image

Use this function to set the image as background. The image is not stretched to fit the dialog box client area. Use the BackgroundLocation values to specify the image location.

uiBmpResIdThe image resource ID
locationThe image location
bRepaintSpecifies whether the dialog box's client area should be updated immediately
bScaleByDPISpecifies whether the image should be scaled according to current DPI