You can use
get_posts or create a new
WP_Query using the following args (or something similar).
$args = array(
'post_type' => 'attachment', // attachment post type
'post_status' => 'inherit', // all attachments have this post status
'post_mime_type' => 'image', // make sure you get images only
'posts_per_page' => 5 // however many images you want
When looping through the images, you can use
wp_get_attachment_image_src to grab the image HTML or image URL respectively.
$attachments = get_posts($args); // args from above
foreach($attachments as $a)
// replace `thumbnail` with an appropriate image size
echo wp_get_attachment_image($a->ID, 'thumbnail');
You'll also want to read up the widgets API for creating widget. The codex has a basic example. There's also quite a few tutorials out there, here's one I wrote.