Unwanted Image Compression

Hi,

I am trying to figure out the optimum file sizes for the images on my website: alexandbabi.com

I have been saving my images as files ranging between 50 to 100 KB with the best quality for size trade off. I noticed though that wordpress is automatically optimizing the images after I upload and insert them. For example, I just uploaded a 1.3 MB image just to test, and I ended up with an image that was slightly above 100kb. Where is this optimization happening and how can I control it??

Thanks,

Alex