How to display the number of images contained in a node using Views?
Install the module: Field Count Formatter 


  A very simple module to provide a formatter for all field types. The
  output is simply a count of the number of items in that field. This is
  most useful on fields which have multiple values as it will show how
  many values are in this field.


Then in the teaser display for your content type, add the image field and set the formatter to count.