It's pretty hugs, but it depends on which version of SQL Server you have - the Express version for example is generally restricted.
The "Normal" limits are here: http://technet.microsoft.com/en-us/library/ms143432(v=sql.105).aspx
] - there is a drop down for the different versions 2008R2 / 2008 / 2005
But...you will start to use server bandwidth pretty quickly if you aren't careful, which can slow things down a lot - I'd be tempted to keep them as files in a suitable HDD and store the path to the image in the DB instead. That also makes it easier to do regular (non SQL) backups, as you don't need to copy a single multi-terabyte file...