One very effective look for images, regardless of whether you are preparing your graphic for print or for the web is changing the used colours to limited palette such as in using mono- or duotone images. Just to remind you – here is quick break down of the technique:

1. open your image in Photoshop – here the image used is that of a yellow flower on dark coloured rock. Though the contrast within the image is quite vibrant and effective – the aim is to tone this down and edit the image to be used as background graphic, tied into the colour scheme of a site design, for example.
   
2. In order to edit this image as duotone – you will need to make sure that the image mode is set to 8Bit/Channel – and turn the image into a grayscale image.
   You could simply go to the top menu, select image and mode > and choose the grayscale option.
   However, it would be best to fine-tune your image using the channel mixer adjustment layer – rather than choosing this automated conversion only.
   
3. to apply the channel mixer options – go to the layer palette and create a new adjustment layer. The setting window will open – allowing you to edit each channel’s percentage setting. To achieve a black and white image, ready for grayscale mode, check the ‘Monochrome’ box in the bottom left corner.
   You can now edit the colour information of each channel separately which will allow you to achieve richer and more defined grayscale image to use.
   
4. Once you are happy with your adjustments – click ‘ok’ to confirm. Now you are ready to turn the image into grayscale using the top menu, as mentioned above.
   top menu > image > mode > grayscale
5. You can now turn your image into a duotone image.
   top menu > image > mode > duotone
   
   select duotone form the drop down menu and click the Ink 2 colour icon to select your chosen colour.
6. Again, you have an option to fine tune this effect – by clicking on the curve icon you can edit the way the duotone effect is applied to your image.
   
7. You should now have a nicely shaded duotone image ;)