All modern web browsers support the webp image format: https://developers.google.com/speed/webp However, Libre Office Writer doesn't support webp. Therefore, you cannot copy an image off of a webpage that is webp and paste it into a LibreOffice Writer document (like you can with PNGs). Here's a webpage containing several images in webp format: http://www.amorosity.com/SlingBlade/ To reproduce, simply right-click on one of those images, copy it, and then attempt to paste it into LibreOffice writer. While this works with PNGs, it doesn't work with webp.
*** This bug has been marked as a duplicate of bug 114532 ***