You can use GIMP, a free graphic design program, to merge and edit pictures. GIMP allows you to maintain separate layers within one file, enabling you to insert a cropped face, for example, and position it over a pre-existing head within another image. You can use GIMP to isolate, resize and recolor the face as well, producing professional, polished results.
Launch the free software; click "File," then "Open." The "Open Image" dialogue will appear, letting you click on the file of your choice. Choose the image you want as your background and press "Open" when finished. Your file will appear in a GIMP workbook with the main toolbox appearing as its own free-standing dialogue.
Click "File," then "Open As Layer." Select the file name of the image that contains the face you want to put on the background head and press "Open." The face image will be inserted as its own layer, meaning any action you implement will only affect the face layer and not your background image.
Click "Layer," "Transparency," then "Add Alpha Channel" to add a transparency channel to your face.
Locate the "Eraser Tool" in the main toolbox; click on the corresponding icon and increase the "Scale" to a size that suits your image. Double-click and drag your cursor over any area you want to remove from the foreground. Zoom in to view intricate details by locating the "View" box at the bottom of the workbook and selecting an option such as "200%" or "400%."
Click on the "Move Tool" in the main toolbox and double-click and drag your face image to the background head. Nudge the image by using the arrow keys on your keyboard.
Shrink the face, as needed, by clicking on the "Scale Tool" in the main toolbox and clicking again on the face image. A "Scale" dialogue will appear; adjust the width and height according to your preferences.
Select "Color" and "Brightness-Contrast" to adjust the colouring of the face, if desired. Use the accompanying scroll-bars to set your levels until the preview is satisfactory. Press "OK."
Save the multilayered image by selecting "File" and "Save As." Use a picture file extension such as ".jpg" or ".png" to complete the process.
If you save your file using an extension that does not support multiple layers, you will be prompted to export your image so a flattened version can be saved.