I reported this bug in 2.8.7 on the forums at http://forum.openx.org/index.php?showtopic=503490411
and many people have also found it, so it was suggested I report it here:
I recently upgraded from 2.8.5 to 2.8.7. On 2.8.7, though we can save new images without receiving any error, and a new file name for them is then shown, the images are not then shown. On investigation the files have not been created in the www/images directory within the OpenX install. This is where they are meant to be created, as when I test out the invocation code it attempts to serve them from there. www/images has all permissions granted - 777 - with root:wheel ownership.