I use Xing to manage some of my business contacts and even some friends have profiles there as well.
The default size of contact's pictures displayed on one's Xing homepage is 18x24px. On a higher dpi screens, you can thus barely recognize the person shown. As there are multiple sizes of all images available, it's pretty easy to just take (for example) http://www.xing.com/img/users/d/f/1/f34814409.5648827_s1.jpg, remove the _s1 and see a 140x185px version of the picture.
So, everytime I now hover my mouse over a tiny Xing thumbnail, it will show the "full resolution" version of the image. Simple, efficient.