Dealing with missing images
I do all images through a macro, that substitutes in our logo if an image happens to be missing.

{% macro imageTransform(image, transform, caption, extraHTML) %}
  {# Fallback to our logo if the image is null... #}
  {% if not image|length %}
    {% set image = craft.assets.id('84').first() %}
  {% endif %}
  &lt;img src="{{ image.getUrl( transform ) }}" width="{{ image.getWidth( transform ) }}" height="{{ image.getHeight( transform ) }}" title="{{ caption|default('') }}" alt="{{ caption|default('') }}"{% if extraHTML %} {{ extraHTML }}{% endif %}&gt;    
{% endmacro %}


We have a more complicated version for responsive images but that's the basic idea...

Also, to find things using assets, although I have never used it, I hear this is good:
https://github.com/iainurquhart/craft_introvert