There are several ways to do this:
Use the "Link to File" option to create a link from your thumbnail image to the full size image, or
Add a new page to your site that includes the full size image. Create a link from your thumbnail image to this page, or
Use the "View Image" object to create a link from the thumbnail that will open the full size image in a separate popup window (WebEasy Professional only)
Solution:
The following instructions describe the use of the "View Image" object in WebEasy Professional. When you use your own images, make sure the image names are all lower case, and consist of only letters, numbers and underscores. No spaces or other punctuation.
Use the photo browser to go to the "Objects\Objects - Advanced" folder.
Drag the "View Image" object onto your page
Go to the "Photos\Beach" folder and drag the p10002 image on top of the View Image object so that it replaces it.
Select the now altered View Image object and click the Link button in the top toolbar
Change the Script so that it starts as follows:<a click="var ixni='p10002.jpg'; eval(window.......
Click OK.
Drag the p10002.jpg image onto the page again, so that you now have two copies of the image on the page - one as the View Image object, and one separate.
Select the second p10002 image and click the "Link" button in the top toolbar
Select the "Internet" tab
Select the "File" button
Click the little browse button next to the "File Name" box to locate the p10002.jpg file.
Click OK.
Resize the second p10002 image so that it's smaller than the View Image one.
Right-click the second p10002 image and select "Order -> Send to Back"
Drag the second p10002 image so that it's behind the View Image p10002 image.
Go to the "Build" menu and select "Preview".
Click the "Options" button
Check the "Dynamic HTML" box
Click OK
Click OK again to preview your site.