Class image alignment help

I was wondering if anyone has a few minutes to clear up an issue for me? Below is *layout.css* (a portion of) that contains the image classes. My question is... how do I add a class to drupal/marinelli so that only the images that are uploaded via filefield/imagefield and imagecache are "float: left;".
-As it is, the default class is #primary img, I have added a "float: left;" to this class, so every image floats to the left... What do I do? I am terrible at css, so im sure there is something that someone could help me with.. Thanks in advance.

#primary img {
margin: 0 15px 0px 0;
padding: 4px;
float: left;*******************-------->I have added this
}

#primary .singlepage img.destra { /*use this class to align images to the right*/
margin: 0 0px 0px 15px;
padding: 4px;
float: right;
}

#primary .singlepage img.sinistra { /*use this class to align images to the left*/
margin: 0 15px 0px 0;
padding: 4px;
float: left;