Many users are reporting that after upgrading to iOS4 that photos on the device appear corrupted or blurry. The fix is relatively easy and outlined below.
The cause of the blurriness that some people have noticed after upgrading to iOS4 is not clear. It appears to me that the photos may be getting optimized more that once and thus degrading the image quality.
Your original photos are safe and sound on your computer. To fix, just resync your photos to your computer.
1. Connect your iPhone to your computer and load iTunes
2. Select your device in the left sidebar
3. Click the Photos tab
4. Uncheck the Sync Photos check box
5. Press Sync to remove the photos from your iPhone
6. Once your sync is completed, recheck the Sync Photos check box
7. Press Sync to return your photos to your device.