Yes, with a very generous limit. You can compress up to at once, with a maximum total size of 5MB per upload (or 20MB via the API). For 90% of casual users, this is unlimited.
If you want a free, open-source alternative to Photoshop that handles JPGs perfectly, (GNU Image Manipulation Program) is your answer.
: Best for JPG vectors, PSD files, and commercial-ready graphics.