Anyway here are some of the tips:
1. If you want to use big resolution image try to slice it in smaller pieces. In this case make sure that the slices will load in away that makes appear gradually to look normal in slower internet connections.
2. Use it in lower quality. In photoshop the option of saving photos for web is an excellent way of having light images with lower quality and without loosing the good look! (I use 65% in JPG format and selective number of colors in GIF images).
3. Using personalized text over. This differs from a case to another, whether text can be big, small, solid, transparent... etc.
4. Glowing edges for non isolated photos is a way to adapt the photo on your background.
5. If you have to use it without cuts try to make it in smaller size and if it's possible to incline it for some degrees right ir left.
6. Editing the background for isolated images is fundamental to personalise the image and make it difficult to be cleaned again.
7. If it's possible to use different brightness and contrast from the original photo. Of course gama and saturn corrections are possibilities also.
8. Using vector shapes suitable to your design over or around. Like adding frames, lines, categories... etc.
What you should not do?!...
Putting any watermark over the downloaded image saying it's your copy right! (Unless you bought the rights of course)
Thanks for reading... Cheers ;)