Textbox

Hi there!
When I run the mouse over my thumbnails I get a little text box, showing the filename. How do I change it, to make is show Tags or Description??

Same problem when the slideshow is running – the filename is shown in the bottom, along with the description. The file nr is not interesting for my visitors – how do I remove it??

My site: http://www.perhallum.dk

https://ww.wp.xz.cn/plugins/nextgen-gallery/