I would like to know which is the best web hosting provider for sites similar to Flickr. The web app will be having more Image uploading/processing functions?
I can recommend Nirvanix (http://www.nirvanix.com/). They have very nice API which allows you to do image processing on their servers (so on uploaded images).
Image hosting is expensive. My suggestion is that you use a CDN for your static, binary conent. You can start with SimpleCDN, which is utterly cheap, and hosting the rest of your site on your own server(s).
I was going to mention Amazon S3 .. look into that for storage
I will check simplecdn. btw, does anyone know where do 'Daily Booth.com' host their server?
A lookup on their ip says rackspace.com does.
You really should be able to find out stuff like that on your own, without asking anybody.