In photography, a 4-by-6 photo is 4 inches tall and 6 inches wide, and a 6-by-4 photo is 6 inches tall and 4 inches wide. Because the different sizes come from a camera held horizontally or vertically, respectively, converting from one orientation to the other without distortion requires creative manipulation. You either need to make the image larger and crop it or resize and add a border around it. You can do both in most image manipulation programs.
Open the 4-by-6 image in an image manipulation program, such as Photoshop.
Select the "Resize" menu usually found under the "Image" menu. Enter "9 inches" for the horizontal measurement and "6 inches" for the vertical measurement. This resizes the photo to 9 inches wide and 6 inches tall. Click "OK."
Select the "Crop" tool. With the crop tool, you select part of the photo, and the tool discards the rest. Click on the top of the photo and drag the crop box down to the bottom of the photo. Drag it sideways until the box is 4 inches wide. Click on the photo and drag it around inside the crop box until the picture pleases you. Click "OK" to crop the photo. When cropped, the photo becomes 6-by-4.
Open the photo in an image manipulation program.
Open the "Resize" menu usually located under the "Image" menu. Enter 2.66 for the vertical measurement, and enter 4 for the horizontal measurement. Uncheck "Resample Image." Click "OK."
Open the "Canvas Size" menu usually located under the "Image" menu. Change the height to 6 inches. If desired, change the colour under the "Canvas Extension Color" drop box. Press "OK." After pressing "OK," the photo resizes to 6-by-4. The original photo appears centred between a bar of colour above and below it.
Some image editing software such as Photoshop cost over £390, but you don't need to spend that much for quality editing software. Consumer Research named GIMP, a free program, one of the top five programs on the market. Download it for free using the link in "Resources."