[Plugin: NextGEN Gallery] Center the images in a Nextgen Slideshow

Try this. Find in CSS

.ngg-slideshow {
    overflow: hidden;
    position: relative;
}
.ngg-slideshow * {
    vertical-align: middle;
}

And replace with:

.ngg-slideshow {
   width: 100% !important;
}
.ngg-slideshow * {
    margin: 0 auto !important;
}
.ngg-slideshow img {
    position: relative !important;
    display: block;
}