Image effects are not displayed in Confluence 5.5 or later
Image effects (such as blur, taped, shadow) do not appear on a page or in the image properties dialog.
Displaying image effects can be memory intensive, and has been known to cause out of memory errors. Confluence 5.5 and later limits the threads that are dedicated to displaying image effects so that it does not impact your whole instance. When there are no threads available, Confluence will display the image without the image effect.
If this issue occurs all the time regardless of the load in the Confluence it is probably cause by corrupted file in the Confluence installation folder.
If you regularly encounter this problem you can add the following arguments in the JVM options to adjust number of threads and queues. (Please see this documentation
Configuring System Properties on how to configure these)
-Datlassian.image_filter.thread_pool_configuration.core_pool_size = 4 -Datlassian.image_filter.thread_pool_configuration.max_pool_size = 4 -Datlassian.image_filter.thread_pool_configuration.queue_size = 10
Reinstall the Confluence using a newly downloaded installation file.