Theme Modification

I am working on a major revision of my video blog and I made it so that 20 posts appear on a page, each within a table of five rows, with 4 columns each. I was curious if there is an easy way to make it so that images for the related video are within the link to lead to the post. Clearly I need something automated because editing each page every day would become a hassle. Is there an image property for a post though? Or a way that I can make it so that an image is related to each post?