Post with image

Hi everyone.

I desperatly need help with images in my posts.
I want to assign a category images automatically to each and every post i make. I wrote this line within the exerp

<img src=”http://url.com&lt;?php echo the_category_ID() ?>.png” alt=”Category: <?php the_category() ?>” />

It works fine exept two thing.
1. I use different categories and some news-items are posted in multiple at the same time. For example news (main category) & politic (sub category) or entertainment (main category) & film (sub category).

Now when i select multiple categories the image that shows is the main category. Is it somewhere possible to show the last category checked?

For example (* is selected)
News *
– Politic
– Economic *
Entertainment
– Film
– Literature
– Music

The economic image appears instead of the newsimage?

I also tried the plugin category images but for some reason it doesn’t work.. (no images displayed).