You'll
need to show the Info Pallette. To do this, go to Window -> Show Info.
You'll
also need to set the unit measurement to pixels. To do this, go to File
-> Preferences ->Units & Rulers....
Choose
pixels for the Units in the Rulers section. (Click OK)
Select
the Marquee Tool. This button is in the upper left hand corner of the
Photoshop toolbar.
Decide
on the part of the image that you would like to be clickable. There
are 4 different shapes that HTML allows you to code. The diagram below
demonstrates the different shapes and the coordinates you wil need
for each one.
Record
the coordinates by placing the Marquee tool over the required points.
The info pallette will then display the coordinates in pixels.
Now you
need to add the html code. To define a map and its coordinates, follow
this example: