[xwiki-users] The user portrait displayed in activity stream and comment is small and distorted

Hi all, I found that the user portrait displayed in activity stream macro is scaled smaller with the following markup: <img alt="username" src=" xwiki/bin/download/XWiki/yangli/obamaMao.jpg?width=50&amp;height=50&amp;keep AspectRatio=true" title="username"> However, the quality of the resulted image is very poor and highly distorted However, if we use an alternative as <img alt="username" src=" xwiki/bin/download/XWiki/yangli/obamaMao.jpg " width=50 title="username"> The resulted picture would look much better! The first way saves network flow, however, I prefer better and larger user portrait display. So it seems that I can (maybe cannot) modify the activity stream and comment macro to get a better display of the user portrait, however, the macro is an jar, which makes it a little bit difficult for me. So any suggestions? Thanks all : )