I posted this in another topic, but I'd thought I post it here too. Took me a short while to come up with but maybe it'll help you.
To get an image above the title using custom fields and no plugins do the following:
1- Make a post in wordpress
2- Under custom fields create a key titled "img_post_header" or something similar
3- For the value, insert the location of the image
4- If you want more image atributes (such as alt text), make more keys and remember what they are called
5- Save/publish that stuff
6- Open /wp-content/themes/[themename]/index.php, after the <div class="post"> but before the <h2> title (should be around line 9), add this line:
<img src="<?php echo get_post_meta($post->ID, 'img_post_header', true);?>" width="600" height="200" />
Of course edit width and height to your specifications.
7- For a custom alt attribute, edit the line to add something like this (assuming img_post_header_alt is the key you used in #4):
alt="<?php echo get_post_meta($post->ID, 'img_post_header_alt', true);?>"
If say you wanted to make the post title the alt text do this:
alt="<?php the_title(); ?>" inside the img tag
You should be all good after this.