Do you use ie6?
IE6 is set up to resize the images based on the Display DPI setting. You can either set the DPI to the default (Normal - 96) or remove IE6's UseHR registry
key to deactivate image resizing. Here are the relevant information (from Microsoft
Image Scaling in Internet Explorer (hi-res)
How to Activate Image Scaling
Internet Explorer 6 and later automatically adjusts the scale on higher resolution
systems when the DPI setting is higher than 96 DPI and the "UseHR" registry value
is added to the registry. These are usually done by the manufacturers of higher resolution
Using the Windows Registry Editor incorrectly can cause serious
problems requiring the re-installation of your operating system and
possible loss of data. I do not and will not support problems that
arise from you editing your own registry. Use the Registry Editor and
my directions at your own risk. Be sure that you create a backup of
your registry and be very sure that you know how to restore it. If you
are not sure how to do both of these things then STOP here!! and read the directions.
Set the DPI
These are the steps for changing the DPI setting on your system.
Right-click the Windows desktop to display the context menu.
Click Properties on the context menu to display the Display Properties dialog.
Click the Settings tab on the Display Properties dialog to display the Settings
Click the Advanced button on the Settings tab to display the monitor properties
Select a DPI setting in the Display frame of the monitor properties dialog to change
the DPI setting.
Restart your system to allow the changes to take effect.
Add the UseHR Registry Entry
The UseHR value is added to the Main key under "Internet Explorer" as follows:
Right Click in the right pane and select New>DWORD value and set its data to 00000001
This problem can also be caused by bad video drivers. Update your drivers from
the manufacturers site.