This can be done using DHTML Effects. Many of the available effects (e.g.: fades, wipes etc) work best in Internet Explorer. In Netscape, your photos will just appear one after the other, rather than fading or wiping.
Solution
1) Insert three photos on your page
2) Click somewhere else on the page (not on a photo) to ensure that no items are selected
3) Hold down the CTRL key and click on the photos one at a time, starting with the rear-most photo.
4) In the toolbar at the top of the screen, click the "Effects" button.
5) On the screen that appears, select "Box Wipe - In from edge" from the "Effect" drop down list.
6) In the "Style" list, select "Fade in - Slow"
7) Check the box labeled "Arrange a slideshow of the selected items"
8) Click OK
9) Click "Build" the "Preview" your site. In the Preview web site dialog, make sure that the Heading reads "Dynamic Internet web site". If it reads "Standard Internet web site", double click on the icon beside the heading to change it.
9) You will see the Preview of your site in your Browser. Click on "Refresh" to see the effect again. You should see the photos appear one after another.
10) If you want to try different effects, repeat steps 2 through 7 with different settings.
11) Once you are happy with the effect, select all the photos again as in steps 2 and 3.
12) Right-click on one of the photos and select "Fit -> Make Same Size"
13) Right-click on one of the photos again and select "Fit -> Make Same Position"
14) Preview your site as before.
Of course, you can do this with any number of photos - not just three.
Note: WebEasy Professional includes many more effects than does WebEasy.