Here are instructions I provided in another forum post on a couple of ways to upload an image file to use in your scenario.
Regarding your question about colab vs local—by default, nothing you run in colab is running on your laptop. From their docs:
Code is executed in a virtual machine private to your account. Virtual machines are deleted when idle for a while, and have a maximum lifetime enforced by the Colab service.
There is a way to connect your colab notebook to a local runtime (which I just learned about when googling around after reading your post). I have never had a reason to do so since I don’t have a local GPU and run all my fastai coursework either in Colab or Kaggle.