Hi @thomaslannes
do you also have a link to your website?
LayTheme compresses images that the< are displayed faster on for example mobile devices.
You can deactivate that. But then your images will be quite big.
If an image has max. 4000px and a resolution of 72 dpi it should be more than enough for web.
Have a look here:
0_1513864705717_Bildschirmfoto 2017-12-21 um 14.58.12.png
All the best!
Marius