seooptim.module

<?php

/**
 * Implements hook_filter().
 */
function seooptim_filter($op, $delta = 0, $format = -1, $text = '', $cache_id = 0) {
  switch ($op) {
    case 'list':
      return array(0 => t('SEO Optim Filter'));

    case 'description':
      return t('Make SEO optimizations on content');

    case "process":
    	$text = preg_replace_callback('/<img[^>]*(alt="")[^>]*src="([^"]*)"[^>]*>/', '_seooptim_filter_imgalt', $text);
      return $text;

    default:
      return $text;
  }
}

function _seooptim_filter_imgalt($matches) {
	$src = $matches[2];
	$src_array = explode("/", $src);
	$alt = array_pop($src_array); // get file name
	$src_array = explode(".", $alt);
	array_pop($src_array); // Delete extension
	$alt = implode(' ', $src_array);
	$alt = str_replace(array('-','_'), array(' ',' '), $alt);
	return str_replace('alt=""', 'alt="' . check_markup($alt) . '"', $matches[0]);
}

function seooptim_preprocess_content_field(&$variables) { 
	if($variables['field']['widget']['type'] == 'imagefield_widget') {
		foreach($variables['items'] as $key=>$image) {
			if(empty($variables['items'][$key]['data']['alt'])) {
				if(!empty($variables['items'][$key]['data']['description'])) {
					$alt = $variables['items'][$key]['data']['description'];
				}
				else if(!empty($variables['items'][$key]['data']['title'])) {
					$alt = $variables['items'][$key]['data']['title'];
				}
				else {
					$alt = $variables['node']->title;
				}
				$alt = check_plain($alt);
				$variables['items'][$key]['data']['alt'] = $alt;
				$variables['items'][$key]['view'] = str_replace('alt=""', 'alt="' . $alt . '"', $variables['items'][$key]['view']);
			}
		}
	}
}

function seooptim_preprocess_node(&$variables) {
	foreach($variables as $key=>$value) {
		if(strpos($key, 'field_') !== FALSE && is_array($value)) {
			if(isset($value[0]['fid']) && strpos($value[0]['filemime'], 'image') !== FALSE) { // It's an imagefield
				foreach($value as $itimage=>$image) {
					if(empty($variables[$key][$itimage]['data']['alt'])) {
						if(!empty($variables[$key][$itimage]['data']['description'])) {
							$alt = $variables[$key][$itimage]['data']['description'];
						}
						else if(!empty($variables[$key][$itimage]['data']['title'])) {
							$alt = $variables[$key][$itimage]['data']['title'];
						}
						else {
							$alt = $variables['title'];
						}
						$alt = check_plain($alt);
						$variables[$key][$itimage]['data']['alt'] = $alt;
						$variables[$key][$itimage]['view'] = str_replace('alt=""', 'alt="'. $alt .'"', $variables[$key][$itimage]['view']);
					}
				}
			}
		}
	}
}