Placeholders for missing images

If a data source doesn't contain images for certain items, what is the best way to indicate that the image used is a placeholder image?

The type of placeholder image would probably alter dependant on the type of image that should be there. For example if its a missing image of a person then a silhouetted image of a person would probably be used. But what if its a generic image whereby I don't want to indicate the type of image that's missing, only that this particular item doesn't have its own image.

Any thoughts?

EDIT/ADDITION

Ok lets get into specifics then. Lets assume a placeholder is needed. it has to be a generic placeholder i.e. no human silhouette or identicon or file type. Is the best solution a variation on the flat grey mountain and sun icon? I believe it is but what are peoples thoughts on this?

Answer

I believe it depends on content too much to give a single answer.

what is the best way to indicate that the image used is a placeholder image?

Generally, you want it to be easy to tell the placeholder from the real thing. So if the expected image is a photo, do not use a photographic image as a placeholder, but rather an icon.

Always make sure that the placeholder matches the style and colors of the system, visually showing that this piece of graphic is a part of the program controls, not a part of the user contents, or perhaps just leave the space empty.

Some variations:

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  Layout does not necessarily require a placeholder. Not finding a good example right now, so this menu will have to do:

  
  

  

  
  


• Containers can be used so that it does not matter whether there is an image inside or not (Empty folder below)


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  Icons: could be used, depending on the situation, just like the silhouette you mention, or the Empty Image below:

  
  
  

  

  
  

Edit/Addition (see question)

If the image that needs a placeholder is the type of image that actually could be The Sun and the Mountain, then yes, using that metaphor would work.

If the image, when existing, rather would be a picture of a tool (a hammer), a shape (a polygon, a border, a rounded corner), an organism (an amoeba), then pick another metaphor accordingly.

If you really need a placeholder image/icon for your "generic image", then the job starts in finding that metaphor, and many systems find The Sun and the Mountain appropriate.