Question

I am using a form to upload files(images) to my server. How can I possibly prevent the same image from being uploaded twice?? I cannot possibly look wether the a image by same title exists as same images can have different titles and different images can have same title.
Any help is appreciated.

Answer 1

Create a hash like ZombieHunter suggested. Why? Because is easy and fast to search and check through a big table of hashes if the image already exists. Unfortunately all this hash metdods like md5 or md5_file work on existing files not on remote ones. So you will have to upload the file anyway. What you can do is then decide if you want to keep or not the file. If you are fetching the files from an online resource, maybe there are ways to detect from headers the file size and run a hash without downloading it, but this is a special case.

Also if you have other business logic attached to those images, with concepts like userHasImages or companyHasImages you can organize them in namespaces/folders/tags so you can speed the search even further.

In terms of database strictly speaking prevention of duplicate entries, use an unique index for the column that contains the hash.