This overview is for all users:

• Users are assigned individual permissions to add/remove or just to view media from the medial libraries on a library by library basis.  Several individuals can be adding and removing images to the same library.
  •  It is up to the people adding files to these libraries to ensure that the file names are unique.
  • To replace an existing file, just upload a new file with the same name.
    
    • File names will be converted to Internet standards (e.g., spaces and non-alphabetic characters will be silently converted to the under-bar separator '_').  This can result in two files having the same name after conversion.  
    • If it is an image file and the size of the file has changed, page authors should re-select the image where ever it is used or go the the Appearance's tab in the image selection pop-up and un-check the 'constrain image size' check box so that the browser does not re-size the new image to the old image's size.  'Constrain Image Size' is the default behavior because it results in significantly faster page display times.  This means that is the new version of the image has a different size the browser will force it to fit into the old image's size which will probably cause it to be distorted.
• When a Media Library is created it can be designated as Gallery if the feature is enabled for your site.
  
  • By going to the Mange Media function, user 'Admin' can make a non-Gallery folder into a Gallery. While the thumbnails will be created you must use the "Organize" button to add in the Titles.  The thumbnails are create using the site default width.
  • Galleries can have non-image files in the directory.  However, they will not, as of this writing, be included in a display called out by the '|.gallery or |.galleryDiv tags. 
  • The site designer will typically select the optimum number of images which can be displayed across on a gallery based on the site's gallery's thumbnail width and page layout.
  • The site default maximum thumbnail width is set via the Configuration Function.  The 'Admin' user can change this at any time by changing the thumbnail size on an individual media folder page change the thumbnails in that folder.
  • For certain galleries larger (or smaller thumbnails) may be needed.  If the thumbnails are larger then fewer of them can fit across a gallery.   If they are smaller then more can be fit across the page.  Remember the |.gallery tag only specifies the number of thumbnails across and then down.   The 'Admin' user can go to the Manage Media function and select an existing gallery folder and change the maximum width of the thumbnails.  If this is done the system will pause and replace each of the thumbnails to be re-built from the original images.   Site designers can use this to fine tune the size of thumbnails for the different number of columns used in a site.  |.galleryDiv:LLLL:w:h.| tag can be used as an alternative to generate a gallery using div tag instead of a table structure for responsive designs. The |.galleryDiv:LLLL:w:h.| tag allowS thumbnails to stack in columns when they can no long fit across the page.
  • If there are more images in a gallery folder you need to provide a |.galpages ... tag which will allow the visitor to move between pages within the gallery.

For more details see the section under Administrative Setup