You don’t say if the upload is in admin or on the user side. User side is probably via a plugin, so I have no idea what you are using.
Admin side has a number of hooks related to uploads. Some of them are listed below. Many WP hooks have little or no documentation, so you may have to Read the Source®. HTH
./wp-app.php: do_action('wp_create_file_in_uploads', $file); // replicate
./wp-admin/includes/media.php:do_action('admin_enqueue_scripts', 'media-upload-popup');
./wp-admin/includes/media.php:do_action('admin_print_styles-media-upload-popup');
./wp-admin/includes/media.php:do_action('admin_print_scripts-media-upload-popup');
./wp-admin/includes/media.php:do_action('admin_head-media-upload-popup');
./wp-admin/includes/media.php:do_action('pre-upload-ui');
./wp-admin/includes/media.php:<?php do_action('pre-flash-upload-ui'); ?>
./wp-admin/includes/media.php:<?php do_action('post-flash-upload-ui'); ?>
./wp-admin/includes/media.php:<?php do_action('pre-html-upload-ui'); ?>
./wp-admin/includes/media.php:<?php do_action('post-html-upload-ui', $flash); ?>
./wp-admin/includes/media.php:<?php do_action('post-upload-ui'); ?>
./wp-admin/custom-background.php: do_action('wp_create_file_in_uploads', $file, $id); // For replication
./wp-admin/upload.php:<?php do_action('restrict_manage_posts'); ?>
./wp-admin/custom-header.php: do_action('wp_create_file_in_uploads', $file, $id); // For replication
./wp-admin/media-upload.php: do_action("media_upload_$type");
./wp-admin/media-upload.php: do_action("media_upload_$tab");