Images on the web are different than images for print. The goal is to find a good balance between image quality and file size.
Here are some guidelines for preparing images using Adobe Photoshop
1. Resize your image according to the recommendations for your template.
NOTE: For portrait/vertical images, size image height according to your template specifications and let the width automatically resize proportionally.
2. Make sure your image is in sRGB color space. If not, convert it by choosing Edit > Convert to Profile … and choosing sRGB
3. We recommend performing some sharpening after you have resized your image. Our preferred method is
1. Choose Filter > Sharpen > Sharpen
2. Choose Edit > Fade Sharpen
3. Set the Fade opacity to a value that reduces the sharpening effect to an acceptable level (generally between 50 and 70)
4. Save your image by choosing File > Save for Web (do not use File > Save or File > Save As …)
1. Select JPEG format
2. Make sure progressive is not checked
3. Choose a quality level (generally between 70 and 90)
4. Resulting file size will be displayed in the lower-left of the Save for Web window
5. Click Save to save your file (when saving, avoid special characters in your file name)
Most web browsers do not read or support Color Profiles (except Safari and Firefox 3 with an add-on). But, most displays are very close to the sRGB color space.
So the approach that is the most accepted is to convert the image into that space first (sRGB) to get it as close as it can be to approximate the viewing device color space (the users monitor).
Since the color profile is not read by the browser, the idea is to strip it using “save for web” to greatly reduce the file size.