Instagram keeps more than one version of every published photo, and the largest is not always the one on screen. The image you see in the mobile feed is usually a downscaled copy, generated to load fast — take a screenshot and that smaller version is exactly what you save.
Baixargram fetches the largest version available on Instagram's servers and hands over the file as it lives there, with no re-compression on our side. In practice that means twice the definition of a screenshot or better.
One limit belongs to Instagram, not to us: the platform resizes what is uploaded. A photo published from a large file usually ends up at most 1080 pixels on the long side. There is no way to recover the 4000-pixel original once it has gone through the upload — what exists is the best version Instagram keeps live, and that is the one we deliver.