You can add a grid to a photo printout using a pencil and ruler, but you can digitally add a grid to a photo file on the computer with the basic straight line tool---or its equivalent---offered in just about every design program. Knowing what you want your grid to ultimately look like will help you space the horizontal and vertical lines accordingly, giving you a file you can print out or further use in its digital form.
Open your digital photo using your favourite graphics editor to view it. Almost any design program will do, but selecting one that has an embedded ruler across the top and side of the file can ease the task of adding a grid.
Locate a "Paint Brush Tool" or "Pencil Tool" in the main toolbar and click on it. Looking at the top ruler and side ruler, determine what spacing you will give your grid; for example, you may want to end up with a horizontal line at every inch mark and a vertical line at every inch as well.
Place your cursor at the top of your file where you want your leftmost vertical line to be. Click on the image, holding "Shift" and "Control" as you drag your cursor down a straight path to the bottom of the file, clicking at the bottom. Continue placing vertical lines in the same manner, and then use the approach to insert the number of horizontal lines you wish to feature.
Save your file using a picture extension--such as ".jpg" or ".png"--or a workable file extension--such as ".xcf" in the free, public domain program GIMP--depending on your project preferences.
Locate on your computer the digital image you want to edit, right-clicking on the file name and selecting "Open With" followed by "Paint."
Select the "Line" icon from the "Shapes" toolbar and pick a colour from the "Colors" section.
Place your cursor where you want one horizontal or vertical line to begin. Double-click at the desired location, holding the "Shift" key down as you drag your cursor across the workbook to the opposite side; let go of the mouse and "Shift" key when finished. Continue placing horizontal and vertical lines, spaced according to your preferences.
Save your grid-embellished file using the "Save As" function along with the picture extension of your choice: ".png," ".jpg," and ".bmp" are all acceptable types.
Visit the online editor at LunaPic.com. Select "Choose File" to locate the image you want to work with and click on "Upload Now."
Click on the "Drawing Tool" icon on the left-hand side of the page and select "Straight Line" from the top drop-down box. Double-click your cursor on your image at the location you want to begin a line and drag it across the screen until you have reached where you want the line to end. Select "Apply" after each successful line you draw to save the addition, and continue to draw horizontal and vertical lines until your grid is complete.
Select the "Save To Your Computer" hyperlink to download the image as a ".gif" file to your computer.
To add your grid into your photo file but not directly onto the picture itself, insert a new layer--if applicable in your design program--before inserting the horizontal and vertical lines themselves.
If you do not want to override the original file, use a different name when saving your grid-embellished photo.