Windows XP lets you rotate pictures by either right-clicking on them and clicking "Rotate Clockwise" or "Rotate Counter Clockwise" or by opening them in Windows Picture and Fax Viewer and pressing the corresponding button on the toolbar at the bottom.  However, when rotating certain pictures, a warning message pops up that says,
"Because of the dimensions of this picture, rotating it might permanently reduce its quality.  Rotating a picture automatically saves it using the original name.  To save a backup copy first, see 'Copy an image' in help." 
The first time I saw this was when I got a new, more powerful camera, so I thought it was a result of the image size (5.0 megapixels vs. 2.0 megapixels).  So I lowered the image quality on my camera from "large" to "medium". 

But today I found out that the Windows Picture and Fax Viewer can only losslessly rotate pictures if the horizontal and vertical pixel values are divisible by 16.  This worked for my old 1280 x 960 pictures (divided by 16 is 80 & 60) but not for my newer 2592 x 1944 pictures (divided by 16 is 162 & 121.5).  The solution to this is to download something like the JPEG Lossless Rotator, a freeware utility that "performs a special lossless block transformation" which produces a rotated image with the same quality as the original.  When I used it, it produced a smaller file size, but apparently this is ok (I don't know everything when it comes to digital images). #entertainment