Hosting web site images: Flickr PRO, Amazon S3 or...?

Question

I'd like to save some of my site monthly bandwidth allocation and I'm wondering if I can use Flickr PRO or I should rely on Amazon S3 as an hosting service for my web site images. (My Web Application allows users to upload their own pictures and at the moment it's managing around 40GB of data)

I've never used Amazon's services and I like the idea of using Flickr REST Api do dynamically upload images from my webApp.
I like also the idea of having virtually unlimited space to store images on Flickr for only 25$/year but I'm not sure if I can use their service on my web site.

I think that my account can be banned if I use Flickr services to store images (uploaded by users of my website) that are not only for 'personal use'.
What's your experience and would you suggest other services rather than Amazon's S3 or is this the only available option at the moment?
Thanks

edit: Flickr explicitly says 'Don’t use Flickr for commercial purpose', you could always contact them to ask to evaluate your request but it sounds to me like I can't use their services to achieve what I want. S3 looks like the way to go then...
Even though a rough estimate of what I'm going to spend every month is still scaring

  5000 visit/day
* 400 img/user (avg 50kB/image)
* 30 days
= ~3TB of traffic

* 0.15$/GB (Amazon S3)
= 429$/month

is there any cheaper place to host my images?

Answer 1

400 images per user seems high? Is that figure from actual stats?

Amazon S3 is great and it just works!

A possible cheaper option is Google. Google docs now supports all file types, so you can load the images up to a Google docs folder, and share the folder for public access. The URL's are kind of long e.g.

http://lh6.ggpht.com/VMLEHAa3kSHEoRr7AchhQ6HEzHVTn1b7Mf-whpxmPlpdrRfPW216UhYdQy3pzIe4f8Q7PKXN79AD4eRqu1obC7I

Add the =s paramter to scale the image, cool! e.g. for 200 pixels wide

http://lh6.ggpht.com/VMLEHAa3kSHEoRr7AchhQ6HEzHVTn1b7Mf-whpxmPlpdrRfPW216UhYdQy3pzIe4f8Q7PKXN79AD4eRqu1obC7I=s200

Google only charge USD5/year for 20GB. There is a full API for uploading docs etc

Answer 2

I love amazon S3. There are so many great code libraries (LitS3) and browser plugins (S3Fox) and upload widgets (Flajaxian) that make it really easy to use.

And you only pay for what you use. I use it a lot and have only ever experienced down time on one occasion.

Nivanix is an s3 competitor. I haven't used them, but they have a bit more functionality (image resizing) etc.

Edit:The link about Nivanix is dead now(2015/07/21), because Nivanix was dead.