Hi Wilfried
We use the native uploader of WP under the hood to process the uploaded images.
When images are uploaded, they get automatically resized to predefined smaller sizes for use in various layouts.
This is recommended for performance and is done to avoid loading *all* the images of a gallery in full-res, which could make the gallery very slow, especially when using many images.
If your goal is to allow clients to download images from a collection, there is also a download option in our pro version, which allows them to download full sizes while still using smaller sizes in the layout for optimal performance.
That being said, there *is* a filter to switch the image sizes generation off, if you know what you are doing and are aware of the consequences: https://picu.io/docs/developers/filter-examples/do-not-generate-picus-custom-images-sizes/
Hope this helps!