I see it's already been answered, but see my post here.
Basically rather than use the Worksheet.Pictures.Insert method (which the MSDN recommends you don't use directly, and which returns a raw COM object), try the Worksheet.Shapes.AddPicture method instead.
Dim range As Microsoft.Office.Interop.Excel.Range
Dim pic as Microsoft.Office.Interop.Excel.Shape
Dim filePath as String
range = ...
filePath = ...
pic = range.Worksheet.Shapes.AddPicture(filePath, Microsoft.Office.Core.MsoTriState.msoFalse, Microsoft.Office.Core.MsoTriState.msoCTrue, range.Left, range.Top, 300, 300)
It's not quite as straightforward because you have to specify the exact position and dimensions, but otherwise, pretty cool!