What is the ideal size of the logo and the picture in the author section?

Hi,

Both my logo and author picture on my website http://www.gohappyoffline.nl are not totally sharp, although the images I use are of good quality.
Is there an ideal size of the logo and author picture, like you have for the header and the flavicon?

Or could you explain me how I get these pictures sharp?

Thanks a lot,

Margo Rijerkerk