You don't need complicated software in order to layout a poster-sized photo. You can do this using Microsoft Word, which comes standard on many computers with the Microsoft Office suite and is fairly easy to navigate compared to some graphic design programs. Once the poster is laid out, you can then either print it on a wide format home printer or send it to your local copy shop for production.
Decide on a size for your poster. Open a blank document in Microsoft Word and then choose "Size" from the "Page Layout" menu ("File" then "Page Setup" in some versions). Set the document measurements to match your desired poster size.
Open the file in an image editing program, like Adobe Photoshop. Make sure that the photo is at least 300 dpi (dots per inch) resolution in CMYK mode--full color, best for printing. You can also check the resolution by right-clicking the image's file name in Windows Explorer, selecting "Properties," and clicking the "Summary" tab.
Save the photo as a TIF file in your image editing program. Other formats will work also, but TIF is ideal for printing high quality images.
Set your margins to about 0.75 inch each. Insert your photo into Microsoft Word ("Insert" then "Picture" and find the file).
Right-click the image and choose "Format Picture" or "Text Wrapping" (may differ depending on your version of Word). Choose the option to allow the image to be "In Front of Text." You can move the image around freely this way.
Hold down the "Shift" key and grab a corner of the photo with your mouse. Pull the image until it is at your desired size. Center the image on the page.
Crop the photo if necessary to make it fit on the page. Right-click the image and select "Size" (may be under the "Format Autoshape" option in some versions of Word) then look for the "Crop from" section. Enter the number of inches you want to crop from the top, bottom, left, or right of the image.
Choose a glossy paper that is the size that you chose, as long as your wide-format printer can handle this type of paper.
Click "File" then "Print" on your Word menu. Choose "Properties" next to your printer's name on the drop-down list. Set the print size to match your document size. Change the print quality from "Normal" to "Best."
Things You'll Need
Poster size paper
Wide format printer
Image editing program
Convert the Microsoft Word file to PDF format and send it to a professional copy shop if you don't have the proper printer.