Google has this service called Photos where you can just upload photos and have a photo library. They arrange them by date, you can arrange them in albums and also search them. They did not charge anything for the storage and made it very easy to get more pictures online.
So whey didn't they charge for storage? They likely wanted to have all this data for image regonition training, and for neural network training you need huge amounts of data. By just offering free space for photos to all people, you are certain to get a bunch of picture. And so I also used the service to store my images. The Android app can also directly upload all new images, I took that as a nice photo backup especially on vacation. I started to upload more images, and eventually it turned into a great dump of pictures that were sent in chats.
Recently they have changed their policy, and in six month they will start charging for storage space. They likely now have enough images online such that they can do neural network training with it. This policy change has made me question my usage of the service. And I realized that I wasn't really using it. So I stopped the automatic upload of my data to the service and then wanted to go on and delete all images which are not linked associated with an album. In some of the travel posts I had included a Google Photos album to shore more pictures, and I wanted to keep that.
As there was no option for it on the website, I thought that the API would be a good start. It would be a Sunday afternoon Python project. I started to read the API documentation, downloaded an API key and eventually started looking for a Python library. While reading up on that, I found out that one cannot modify existing content via the API. This means that my whole idea was bust. Other people have requested this feature, but Google hasn't replied there.