Question

If i find an image and copy and paste it into Paint.

Save one version in a Lossless compression format.
Save another copy of the file in Lossy compression format.
What has changed in the Lossy image?

Answer 1

Lossy image formats will remove data during compression as a trade off for lower storage occupation. Lossless data formats will not remove data during compression, resulting in higher quality but also higher storage occupation.

Graphic Artists will almost always use lossless due to it delivering the highest quality image possible.