Recently I needed separate bitmap files for the icons in the Visual Studio toolbox. I took a screen shot and then, rather than splitting the icons apart manually, I wrote this program to do it. The following code does all of the work.

' Split the file.
Private Sub cmdGo_Click()
Dim wid As Integer
Dim hgt As Integer
Dim piece_name As String
Dim num_rows As Integer
Dim num_cols As Integer
Dim row As Integer
Dim col As Integer
Dim X As Integer
Dim Y As Integer
Dim filename As String

    ' Get the inputs.
    wid = Val(txtWidth.Text)
    hgt = Val(txtHeight.Text)
    picWhole.Picture = LoadPicture(txtFile.Text)

    ' Start splitting the Bitmap.
    piece_name = txtFile.Text
    piece_name = Left$(piece_name, InStrRev(piece_name, _
        "."))
    picPiece.Width = wid
    picPiece.Height = hgt

    num_rows = CInt(picWhole.ScaleHeight / hgt)
    num_cols = CInt(picWhole.ScaleWidth / wid)
    Y = 0
    For row = 0 To num_rows - 1
        X = 0
        For col = 0 To num_cols - 1
            ' Copy the piece of the image.
            picPiece.PaintPicture picWhole.Picture, 0, 0, _
                wid, hgt, X, Y, wid, hgt

            ' Save the piece.
            filename = piece_name & _
                Format$(row, "00") & _
                Format$(col, "00") & ".bmp"
            SavePicture picPiece.Image, filename

            ' Move to the next column.
            X = X + wid
        Next col
        Y = Y + hgt
    Next row
    MsgBox "Created " & num_rows * num_cols & " files", _
        vbOKOnly, "Done"
End Sub

Next the code figures out how many rows and columns of smaller images will fit completely within the original image and loops through the rows and columns.

For each row/column value, the code uses PaintPicture to copy the appropriate piece to the picPiece PictureBox and saves the result in a bitmap file.