Need help with CSS and CSS hero

Can you help me create new CSS identifiers for images on my wp posts? I have a logo and image on every post they are being identified as the same thing and I want to edit their size/CSS separately. In wp editor when I select an image and choose to edit it, there are two fields to add new class info for that image. How do I use this properly to make each image unique? The class I set there is not working with CSS hero. It doesn't see it.