Using [ Back Office > Prefences > Images > Regenerate thumbnails ] sometimes, trying to remake the thumbnails for uploaded images, can generate bellow error:
Cannot write “No picture” image to (categories) images folder. Please check the folder’s writing permissions.
Main cause that generate this error message is not necessarily related to the write right (chmod 777) for [ \img ] directory but because of imported language pack that has no [language_iso_code.jpg] file added into the following directories:
An easy solution for this is to copy, lets say [en.jpg] and rename as ISO code for imported language [ex: it.jpg], then upload the file into above directories.