So, and this is an ELI5 kind of question I suppose. There must be something going on like "processing a kazillion images" and I'm trying to wrap my head around how (or what part of) that work is "offloaded" to your home computer/graphics card? I just can't seem to make sense of how you can do it at home if you're not somehow in direct contact with "all the data?" e.g. must you be connected to the internet, or "stable…
The model (presumably some kind of convolutional neural network) has many layers, every layer has some set of nodes, and every node has a weight, which is just some coefficient. The weights are 'learned' during the model training where the model takes in the data you mention and evaluates the output. This typically happens on a super beefy computer and can take a long time for a model like this. As images are evaluated the output gets better the weights get adjusted accordingly.
Now we as the user just need the model and the weights!