import xlwt
from PIL import Image
wb = xlwt.Workbook()

img = Image.open("123.png")
r, g, b, a = img.split()
img = Image.merge("RGB", (r, g, b))
img.save('imagetoadd.bmp')
wsimage = wb.add_sheet('image')
wsimage.insert_bitmap('imagetoadd.bmp', 0, 0)
wb.save('images.xls')