How can Python save a screenshot to a db?

Question

Screenshots

Actually, you need to take a screenshot and write it to Mysql (BLOB)
I know that it is not logical to store images in the database)) but it is necessary
. In Python, do not judge a beginner strictly)
I do this:

#!/usr/bin/env python

import mysql.connector
from mysql.connector import Error
from PIL import Image, ImageGrab
from StringIO import StringIO

def Screen():
    screen = ImageGrab.grab()
    buf = StringIO()
    screen.save(buf,'PNG')
    return buf.getvalue()

try:
    db=mysql.connector.connect(host='x.x.x.',database='test',user='test',password='qwerty')
    if db.is_connected():
        cur = db.cursor()
        data = Screen()
        cur.execute("INSERT INTO ts (screen) VALUES (%s)"% (data))
        db.commit()
        
except Error as e:
    print "MySQL Error [%d]: %s" % (e.args[0], e.args[1])
finally:
        db.close()

displays

MySQL Error [-1]: Failed getting Error information (UnicodeDecodeError('utf8', "Invalid utf8 character string: '\x89PNG'", 32, 33, 'invalid start byte'))

what did you do wrong??