Add watermark to images
I'll focus more on the


  How can I improve my code


part of your question.

Imports at the top

Move your import time to the top of the file, which is standard in Python.

Code in functions

Your logo dimension calculation should be in a function instead of global scope. The code at the bottom should be in a top-level main function.

Integer division

w = int(logo_img.shape[1] * scl / 100)


can be

w = logo_img.shape[1] * scl // 100


Use pathlib

...so that this:

'./test/' + current_object.object_name


can be

Path('test') / current_object.object_name