IS there a filename part or a file extension part that would define the half size that you want? If not, would it be based on the dimensions of the graphic file? I have used command line switches in IRFanView to get graphic size information. There may be an API method that could do it.

The size of the graphic is set in:
[VBA]Set AddPictureUrl = ActiveSheet.Shapes.AddPicture(sLocalFile, msoFalse, msoTrue, picR.Left, picR.Top, 36, 36) [/VBA]

The size of the cell is set in:
[VBA].RowHeight = 36
.ColumnWidth = 6 '6 would be the 36 point. A1 changed to Pic rather than Graphic.[/VBA]