holder.js
function setInvisible(el) {
	    if (!el.holderData.invisibleId) {
	        App.vars.invisibleId += 1;
	        App.vars.invisibleImages['i' + App.vars.invisibleId] = el;
	        el.holderData.invisibleId = App.vars.invisibleId;
	    }
	}
function setInvisible(el) {
	    if (!el.holderData.invisibleId) {
	        App.vars.invisibleId += 1;
	        App.vars.invisibleImages['i' + App.vars.invisibleId] = el;
	        el.holderData.invisibleId = App.vars.invisibleId;
	    }
	}
function setInvisible ( el ) { if ( ! el . holderData . invisibleId ) { App . vars . invisibleId += 1 ; App . vars . invisibleImages [ 'i' + App . vars . invisibleId ] = el ; el . holderData . invisibleId = App . vars . invisibleId ; } }
Sets a unique ID for an image detected to be invisible and adds it to the map of invisible images checked by visibilityCheck

@private
@param el Invisible DOM element
Sets a unique ID for an image detected to be invisible and adds it to the map of invisible images checked by visibilityCheck