Time delay of adding caption to photo slideshow

photos make a great screensaver and the xscreensaver with glslideshow option is what I use. I often use it for ident practice, e.g. plants, birds etc. The image appears randomly on the screen and I think, I know what that is …

At the moment I have various scripts that can create ad-hoc collections of images based on the embedded tags. I also overlay a caption over the images using the convert bit of imagemagick and that works well.

What I want to do is have a time delay so that an image appears for say, 10 seconds, and then a caption appears over it. The filename would be ok. I can control how long the image appears in xscreensaver, and it’s surprisingly easy to train yourself to not-look at the filename or caption, but I’m curious as to whether it’s possible (without too much effort) to add the caption after some time-out period.