Ok we have a photo resized to 8" x 12", but we don't want that. We want a 8" x 10". We can't just type in 10", as that will skew the photo, so we need to crop the width down to 10". So, select the "Crop" tool in the toolbar to the left. It is the third tool down from the top on the left or just hit the "C" key. Look at the photo below.
Ok, now with the crop tool selected, click and drag it over the picture and make sure you don't select the whole image. Leave out some of the edges. Remember we want to get down to 10" from 12". When you are finished either hit "Enter" or right click and select "Crop". Go back to the "Image" Menu and select "Image Size" again and see where you are at. Keep cropping and checking the "Image Size" until you get down to 10" for the width. If you go too far, just hit Ctrl-Z to undo or use the History Palette, if you are familiar with it. If you get really close to 10", just a fraction of an inch away, you can uncheck "Constrain Proportions" and just type in 10. As long as you are close, you shouldn't have any noticeable skewing.

Ok, now you have your photo resized to 8" x 10", we need to rotate it so we can print it. Since you load paper into your printer vertically, you have to rotate your photo to a vertical format. Goto the "Image" Menu, choose "Rotate Canvas" and slide over to "90° CW".
Ok, now our photo is rotated and oriented vertically for printing.

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