Thumbnails resolution

Hello. I have a problem regarding the thumbnails. I can’t seem to get a good resolution out of them. They look right if I open them on any picture viewer but once I upload them they turn blurry. I have tried different formats and sizes. Any assistance would be appreciated.

http://www.pacae.nl/winkel/

http://ww.wp.xz.cn/plugins/woocommerce-dynamic-gallery/