I have the slideshow.css file copied into the theme directory.
What I change in this file (the caption (H4) is no longer displayed)?

I would add it to the theme's css. Look at the page source for the elements to hide. I don't know offhand.

This is a problem, what is the source for element slideshow (macro slideshow)? Theme: zpArdoise

Look at the page source via your browser. All modern browser let you choose even a specific element.

In your slideshow.css add:

`

post #slides h4 {

display: none;
}
`

Thanks!