Usually you have a link to custom gallery like

/gallery/galery_desc_bla-bla/123455/index.html

For rotation purposes we add so called 'rotation parameter'

/gallery/galery_desc_bla-bla/123455/index.html?1x2x1234

where 1x2x1234 is changeв from time to time

But google counts those links

/gallery/galery_desc_bla-bla/123455/index.html?1x2x1234 and /gallery/galery_desc_bla-bla/123455/index.html?2x2x1234

as different pages (and probably dupes)

You can avoid it by adding 'canonical url'

<link rel="canonical" href="http://yourdomaincom/gallery/<!--SAFE_ALT-->/<!--GALLERY_MD5-->/index.html" />
or
<link rel="canonical" href="http://yourdomaincom/gallery/<!--GALLERY_SLUG-->/index.html?video=gallery" />

Hope i've got main idea, so feel free to experiment