Why some pictures in libraries are PSD and others JPEG ?

[Sebastian Mejia]

Its my first time using libraries and I noticed that some of the photos I drag are saved as PSD and others as JPEG, why is that ?

[D Fosse]

An original jpeg will resave as jpeg - if - it still satisfies the jpeg file format specification.

That means no layers, no masks or extra channels, no transparency, no 16 bit depth, no nothing. Jpeg is the most limited and limiting of all file formats, and almost anything you can do to an image in Photoshop will put it outside the jpeg specification. Then it saves as PSD.