Image file sizes

You might be supprised at just how small you can get an image file size and yet still have good quality.
I exported a lot of pics from lightroom a while back with the quality setting on low (somebody else had used it while I was out) Not noticing I then exported a whole batch of pics, it was only later when I went to move the pics I noticed instead of a few GB I had a few MB of images. When I checked the pics were about 200kb each instead of about 5mb. 
Now I'd even looked at the full sized pics and hadn't noticed anything wrong, so I did a few tests.  I tried saving a jpeg at jpeg 2 and the same image at jpeg 12, frankly even at full size I couldn't tell the difference, so then I stacked them as layers, aligned them and set the top layer to difference (to show any differences) while there was a very very faint difference it was bugger all really, certainly nothing you see looking at the image.