You can use the free graphics editor GIMP to merge two digital pictures. Whether you want to overlay a patterned graphic over a photo, or to combine the best of two photos, or to accomplish another merging task entirely, GIMP can help. You can insert pictures as their own separately maintainable layers and edit each layer according to your preferences. When you are satisfied, you can merge the layers to create one final product
Launch GIMP, and open the first picture you want to work with by clicking on "File" and "Open." Locate in your documents the chosen image, selecting it and pressing "Open." Insert into the same workbook the second file you want to include by clicking "File" and "Open as Layer."
Open the "Layers" toolbar by clicking on "Windows," "Dockable Dialogs" and then "Layers." If you want to make the picture you inserted last into a semi-transparent layer over the background, click on the thumbnail that corresponds with the last layer and use the scroll bar at the top of the Layers toolbar to decrease the "Opacity."
Use the "Scale Tool" located in the main toolbar to resize your second image as desired. For example, if your background picture is of a television set, and you want to shrink your second picture so that it looks like it is being displayed on the television, click on the scaling tool and then click somewhere on the picture itself. A "Scale" pop-up box will appear, letting you change the width and height of your picture. If you want to maintain the proportions of the original file, click on the "Keep aspect" box located at the bottom of the main toolbar.
Select the "Eraser Tool" in the main toolbar if you want to eliminate portions of your second image. Before you begin to erase, be sure that your layer has a transparency channel by clicking on "Layer," "Transparency," and "Add Alpha Channel." Double-click your cursor and drag it over all unwanted portions of your image. You can choose the "Brush" type to have a hard or soft edge, according to your preferences.
Click on the "Move Tool" and then double-click on your layer if you want to reposition it. You can double-click and drag the picture across the screen, or you can use the arrows on your keyboard to scoot the image along.
Merge the images once they are situated according to your preferences. In the layers toolbar, right-click on the layer you inserted last and click "Merge Down." If you have more than two layers and want all to be merged, you can instead click on "Merge Visible Layers."
Save your GIMP workbook as a picture using a file extension such as ".JPG."
You might want to save your workbook before you merge the layers as a backup in case you later decide that something about your pre-merged image is not quite right. To do so, save your document using the GIMP-native file extension ".XCF."