' Restrict the form to its "transparent" pixels.
Private Sub TrimPicture(ByVal pic As PictureBox, ByVal _
    transparent_color As Long)
Const RGN_OR = 2
Dim bitmap_info As BITMAPINFO
Dim pixels() As Byte
Dim bytes_per_scanLine As Integer
Dim pad_per_scanLine As Integer
Dim transparent_r As Byte
Dim transparent_g As Byte
Dim transparent_b As Byte
Dim wid As Integer
Dim hgt As Integer
Dim X As Integer
Dim Y As Integer
Dim start_x As Integer
Dim stop_x As Integer
Dim combined_rgn As Long
Dim new_rgn As Long

    ' Prepare the bitmap description.
    With bitmap_info.bmiHeader
        .biSize = 40
        .biWidth = picShape.ScaleWidth
        ' Use negative height to scan top-down.
        .biHeight = -picShape.ScaleHeight
        .biPlanes = 1
        .biBitCount = 32
        .biCompression = BI_RGB
        bytes_per_scanLine = ((((.biWidth * .biBitCount) + _
            31) \ 32) * 4)
        pad_per_scanLine = bytes_per_scanLine - (((.biWidth _
            * .biBitCount) + 7) \ 8)
        .biSizeImage = bytes_per_scanLine * Abs(.biHeight)
    End With

    ' Load the bitmap's data.
    wid = picShape.ScaleWidth
    hgt = picShape.ScaleHeight
    ReDim pixels(1 To 4, 0 To wid - 1, 0 To hgt - 1)
    GetDIBits picShape.hdc, picShape.Image, _
        0, picShape.ScaleHeight, pixels(1, 0, 0), _
        bitmap_info, DIB_RGB_COLORS

    ' Break the transparent color into its components.
    UnRGB transparent_color, transparent_r, transparent_g, _
        transparent_b

    ' Create the PictureBox's regions.
    For Y = 0 To hgt - 1
        ' Create a region for this row.
        X = 1
        Do While X < wid
            start_x = 0
            stop_x = 0

            ' Find the next non-transparent column.
            Do While X < wid
                If pixels(pixR, X, Y) <> transparent_r Or _
                   pixels(pixG, X, Y) <> transparent_g Or _
                   pixels(pixB, X, Y) <> transparent_b _
                Then
                    Exit Do
                End If
                X = X + 1
            Loop
            start_x = X

            ' Find the next transparent column.
            Do While X < wid
                If pixels(pixR, X, Y) = transparent_r And _
                   pixels(pixG, X, Y) = transparent_g And _
                   pixels(pixB, X, Y) = transparent_b _
                Then
                    Exit Do
                End If
                X = X + 1
            Loop
            stop_x = X

            ' Make a region from start_x to stop_x.
            If start_x < wid Then
                If stop_x >= wid Then stop_x = wid - 1

                ' Create the region.
                new_rgn = CreateRectRgn( _
                    start_x, Y, stop_x, Y + 1)

                ' Add it to what we have so far.
                If combined_rgn = 0 Then
                    combined_rgn = new_rgn
                Else
                    CombineRgn combined_rgn, _
                        combined_rgn, new_rgn, RGN_OR
                    DeleteObject new_rgn
                End If
            End If
        Loop
    Next Y
    
    ' Restrict the PictureBox to the region.
    SetWindowRgn pic.hWnd, combined_rgn, True
    DeleteObject combined_rgn
End Sub