When an uploaded image is used in various places throughout your website, the system creates copies of the image in the correct size for the specific page or thumb. Images can be uploaded in these formats: PNG, JPG, GIF  

PNG and GIF images will not darken when resized.  JPG images tend to darken with each resize.  

Here are some hints for maintaining the original appearance of the image:

• Upload PNG or GIF format
   
• Upload JPGs smaller then the Photo Maximum Size in All Tasks > Web Site > Global Settings > Media Settings
   
• Resize JPGs to the exact size required for the template before uploading.