<p>There are several web applications which allow you to send photos from your mobile phone and post them to web site/application. How do these work and what sort of technologies would one use to implement such a feature?  Is it an MMS server or does one need to get into socket programming?  For example, some applications provide you with an email address to email your photos to via mobile phone.  I'm curious to know how these things work.  I can somewhat figure out on my own how they work, but I would like to know this feature is normally implemented. </p>

<p>Thanks</p>

I think you have three options to support this:
MMS - you would need an
MMS gateway
to recieve MMS messages. This can be software/hardware that you run yourself, or there are services were you pay per message. You would likely need to write your own handling of the message at the application end.
Email - you just provide users with an email address to send picture to and you either interface with the email server via POP/IMAP or with the message store directly.
Web form - you implement a web form specifically designed for mobile devices that lets them upload pictures. In truth I have no idea if and how many devices support
```
<input type="file" />
```
, so this may not actually be an option at all.
You can use whatever server-side technology you prefer for processing each of these.