Good, I found it !
Thanks you very much !
(it was in Settings -> Uploads)
I have a few users (including myself) that are experiencing issues with the image upload.
The images start to upload then stop like...
Images do however successfully arrive on imgur.
This started about 2 months ago.
NodeBB version 1.4.2
Any one else experiencing this issue?
Any suggestions of what I can try?
I solved this by installing SSL as that allowed the ws connection to work properly through the ISP in question.