For few products images are visible but for some products images are not visible. After spending few hours i found that for the products whose images are missing is because their images are not getting cached, i cross checked the cache directory under media/catalog/product/cache
Images are not getting cached for few products only and for others images gets cached.
777 permission is given to all media directories.
These products are created programmatically
Best Answer
Check for all browsers/ check your memory limit for
php_value memory_limit256M