Any submission can be embedded on the website of your choice. Each submission has its embed code listed with it. For example, take a look at Deon De Lange's 'Photographer ID' submission from the Pretoria photomarathon in 2007. In the bottom right, underneath the submission details, the section Embed and share shows the code needed to embed Deon's image on another website. It looks like the code below.
<img src="http://photomarathon.eu/s/884/640/427/" />
Simply embedding this line of code on your website results in the image being shown. It will look something like what you see below.
You can even define the size of the image you're embedding. Of the three numbers in the link to the image, the first identifies the individual submission, the second defines the height, the third defines the width. So, you could also do the following, for example.
<img src="http://photomarathon.eu/s/884/1280/128/" />
If you set the width or the height to 0, the width or height is proportioned relative to the height or width, as in the example below.
<img src="http://photomarathon.eu/s/884/240/0/" />