"but is there a way to display only images, and not the text"
A couple ways to do this are:
1. Keep the_excerpt() in place and insert the image in the excerpt field of your post as well. This is a bit of a hack, and can cause problems elsewhere (especially if you display summaries in your syndication feeds). But it works; well enough.
2. Parse the post content for an img tag, and display only this. Something like the following (used in place of the_excerpt() or the_content()) should do:
<?php
preg_match('/<img[^>]*>/i', $post->post_content, $image);
foreach ($image as $display) {
echo $display . '<br />';
}
?>
You might even choose to display an excerpt (or post content) if no image is found in a post:
<?php
preg_match('/<img[^>]*>/i', $post->post_content, $image);
if($image) {
foreach ($image as $display) {
echo $display . '<br />';
}
} else {
the_excerpt();
}
?>