Try
cell = sheet.Cells(1,1)
pic = sheet.Pictures().Insert(r"G:\logos\Logo.jpg")
pic.Left = cell.Left + 20
pic.Top = cell.Top + 30
which will position your picture at 20 pixels right and 30 down from top left corner of given cell.
Regarding help, my reference is search for "excel interop " such as "excel interop range" or "excel interop picture" which leads to Picture object docs.