if these are pictures that you synced from your computer to your iPhone, the best thing to do is get a 3rd party application...Googling is they way to go to search for one.
you can try emailing each picture to an email account on your computer, but the picture's resolution gets seriously degraded
You can use 3rd party software such as TouchCopy (Google it). Be aware that as part of the transfer process to the iPhone, the pictures were 'optimized' = reduced in resolution. You cannot get the full res pics from the iPhone. Another option is to email them to yourself one by one. That results in even further reduction in resolution (down to 640x480 pixels).
The iPhone is not a backup device. I'd strongly recommend considering an external hard drive and Time Machine once you're back up and running.
The iPhone is not designed nor intended to be a backup storage device, and should not be considered as such.
Your iPhoto library should have been included with your computer's backup of other important data.
The sync process for photos is a one way transfer process only - from your computer to your iPhone, and photos transferred from your computer to your iPhone via the iTunes sync process are optimized for viewing on your iPhone as part of the iTunes transfer process so the original resolution of the photos is reduced and lost.
There are some 3rd party utilities that provide for this, but such utilities are not supported by Apple, and the original resolution of all these photos will be lost.
like neuroanatomist mentioned above, the pictures get optimized...and if im stating this right, the pictures basically get optimized when you transfer to something like emails as well, so you "double-optimise" the picture causing the picture quality to worsen.'
For the same pic from my iPhoto library:
• Original full-res pic in iPhoto - 2288x1712 (4 megapixels)
• Optimized pic stored on iPhone - 910x637 (0.6 megapixels)
• Pic emailed from iPhone to Mac - 640x479 (0.3 megapixels)