I did try and tidy up my image paths in a similar way a while ago when I first started using Symfony, I wanted something similar to what you are describing, however I don't think it is possible.
As far as I'm aware I don't think you can set the output of all the images to a single folder (like /images/) - the only way I could get them to be placed in a set folder was to load each image individually with Assetic -
{% image '@AcmeFooBundle/Resources/public/images/example.jpg'
output='/images/example.jpg' %}
<img src="{{ asset_url }}" alt="Example"/>
{% endimage %}
But obviously this isn't very practical.
I would personally let Symfony use it default paths and not worry too much about it, if you really wanted to shorted your image paths maybe you could use a url-rewrite in your public folder?