Q: Gallery: Caching active - deleting images and creating new images
A: This is how to avoid problems when deleting images and using new ones in the gallery when Joomla caching is active
The situation is the following:
The Joomla cache is activated.
In a existing gallery, you are deleting existing images. Next, you are copying new images into the directory in which you've deleted your images.
In this case, the new images will not be created immediately, since the cache is activated and the cached version will be loaded.
There are 2 possible solutions for this:
You can either wait until the Joomla cache expires (which could take some time...)
Or you can delete the Joomla cache (System->Purge cache) and browse again to the gallery.
Now, the images will be created correctly.
This FAQ article applies to the galley module and the gallery component.