What is the Compression Algorithm used by Facebook? I would like to know what is the Compression Algorithm used by Facebook for compressing the images? I uploaded a image of size 242 Kb and I downloaded the same image from my Facebook album. The size of downloaded image is 46 Kb and the subjective quality is similar, I wasn't able to differentiate between the original (uploaded) and downloaded (from Facebook) image. The downloaded image was downsampled though, from 1226 x 1600 to 552 x 720. So Facebook compresses the image at a good ratio while we are uploading it to our Facebook account without affecting the subjective quality much.

I wonder what compression algorithm they are using for this purpose. What would be your best guess?

                           Original image: tamil_girl_painting (size 1226 x 1600)




                  Downloaded (from Facebook) image: tamil_girl_painting (size 552 x 720)
From the images you posted its quite clear that the image has been downsampled and re-compressed with lower quality jpeg settings.  If you look round the mouth you can clearly see JPEG-like artefacts.