Meh, I agree you can't always see the difference - it really depends on the picture and it's especially bad for 'simple' pictures (large areas with the exact same colour) as it was designed with photographs in mind. Just saying what's technically different... you can also find some good information
here. I personally use JPG when putting a picture online because it's small, but it's nice to know that your stored files are perfect, and with storage capacity these days it's not a big issue

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I don't know if JPG is the cause of the 'bad quality' in the picture above, but at a little over 19 KB there's not much data in there. Is there any chance you can do it over with a different format NippelSpanner?