In addition to Adobe Photoshop's vast array of photographic and graphic-editing tools and abilities, the program also allows you to combine images and photographs to create layouts, Web designs and other compositions. You can place two images side by side in Photoshop without resizing or resampling them, and save your composition as a new document, creating the side-by-side image and preserving your two original images.
Open the first image you want to use in Photoshop by clicking "File" > "Open" in the menu bar. Open the second image the same way.
Note the width and height of the first image by selecting "Image" > "Image Size" from the menu bar. Repeat this with the second image. Add the two width figures together and note the larger height figure, if the heights of the images are different.
Select "File" > "New" from the menu bar to create a new document on which your images will be placed side by side. Enter the sum of the two image widths in the "Width" field, and enter the larger of the heights in the "Height" field. Make sure the units in the drop-down menu at the right of the fields match the units you noted in Step 2. Click "OK" to create the document.
Select the "Move Tool" from the left-hand toolbar and click on the window or tab for the first image. Click and drag the image to the window or tab for the new document, and release the mouse once it is on top. The image will appear in its original size, as a new layer, on the new document. Repeat this with the second image.
Click and drag the second image, which will be automatically selected in the Layers palette at the right of the Photoshop window, to the desired side of the canvass. Select the first image layer by clicking on it in the Layers palette, and click and drag it to the opposite side, making sure the edges of the image correspond with the edges of the document. Once you have properly positioned both images, they will appear side by side in their full original sizes. Save your work.
The latest version of Photoshop, as of March 2011, is part of the Adobe Creative Suite 5, but the steps to place images side by side in CS3 are the same.