Images and photographs make sites richer and more interesting.   It is necessary that they are related to the message the page is presenting.

If they are not related to the message they are better not used, since they can confuse a user and distract his/her interest for the page.
 
Most web pages need interesting, attractive and informative images to keep the attention of the user.
 
There are specialized web addresses where you can download images for free or for a charge. Some of those addresses are:
 
www.PhotoDisc.com
www.EyeWire.com
 
Images and photographs can also be inserted into a page by scanning the existing or taking new pictures with a digital camera. Those are probably better methods to insert specific images needed to develop instructional materials.
 
Besides using an image as a link, it can also be mapped, which means that certain sections of the picture will be appointed certain links. By clicking on the chosen sections of a mapped image, other content-related web pages are opened.

Photographs used on the web should be shrunk to a 72 dpi (dot per inch) resolution, since that will make the photograph open faster and maintain sufficient quality on the screen, even though the quality of the picture print will not be good.

You should use images no larger than 400 pixels since most of the screens still have 800x600 pixel resolution and laptop screen resolution is also 800x600 pixels. Besides, by enlarging the picture the time needed for the page to open becomes longer.

Graphic formats for pictures put on the web pages are GIF, JPEG, PNG, SWF.
 
The first two are used most often.
 
GIF is short for Graphic Interchange Format. Image made in a GIF format is compressed, and this format is used for illustrations and logos.
 
JPEG format (Joint Photographic Experts Group) is used for photographs, since it enables the saving of a greater colour spectrum.
 
Before putting a picture on the web page it can be processed in Photoshop or a similar graphic program. The most common tool used for that purpose is cropping, through which the most important part of the picture can be singled out and space on the page freed, making its opening quicker. There are also other options such as changing the colouring (hue/saturation), brightness, contrast and filter (poster, edges, watercolour...). 

Separating the image from the text makes a better effect and it can be achieved by adding space around it or by shadowing, trimming or rotating the image.

The mentioned processing gives a page a more interesting and casual overtone.

Links to examples we used:

PhotoDisc (page specialized in photographs) EyeWire (page specialized in photographs) Citologija (Cytology; teaching-specific pictures) Innerauto (mapped pictures)