Labels.txt has CMOD 644 which is impossible to change via FTP. I contacted the serverhost. They said that it was genereated bij a php script in Joomla and that it cannot be changed by a FTP user. They could change the ownership to my account. Is that a wise thing to do????And do I have to ask the serverhost to change the settings each time i add a new image folder??

As it is said at SIG PRO documentation:
You also have to make sure that Joomla's /cache folder is writable, in other words, check that the permissions for this folder are 755 or 777.