Hi Manuel Leduc 

Thanks for looking into this. I've tried adding an image on a new and existing page; from dragging an image in, copying and pasting content from a Word doc, and inserting the image directly via the Image macro > Upload > Insert. Unfortunately I'm getting the same result each time.

I think I may have figured it out though... we changed our default syntax to Markdown (by installing the CommonMark Markdown 1.2 extension). If I change it back to XWiki 2.1, I'm able to resize the images as expected and get a message that 'WYSIWYG editor has been updated'. 

We do like having Markdown as the default editor (it's been requested by our IT staff). Is this something that would need to be fixed with the Markdown extension or with the wiki editor? 

Thanks!