Making Certificate in Gimp is very easy. You just need to follow all the steps given below and you are done. For this you just need to have an image editing tool, named Gimp. If you don’t have it in your system, just install it with the issuing following command on terminal :
sudo apt-get install gimp
After you are done with installation, lets start with making the certificate in it.
Open the Gimp Image Editor. Then go to file > New. A dialog box opens up. It ask you for the size of image you are making. Pick up the size you want for your certificate. I am selecting here A4 size under template and is orientation as Landscape. See the image below
Now you have to select the background color of your choice, for your certificate. You can also go on, with having a gradient of any shape. Her I made a Radial gradient. You can do this by selecting the gradient tool in the Toolbox.
No certificate is complete without a border. For making a border, its wise if you create a separate layer for it. For this go to Layer> New and then select the transparent layer
Now make a border on the transparent layer we made. For making the border, go to Select > All. Then again go to Select > Border. This opens a dialog box named Border Selection. Here you need to give the width of border to be created.
Now give the color of your choice to the border using Bucket Fill Tool in Tool box.
Then, next you need to insert a watermark image in your certificate. For this go to File > Open as Layers, this will prompt you to browse and upload the image for your watermark. Always choose the image with transparent background and then scale it according to the requirement.
Now add the text to the certificate using Text Tool. Select Font, Size and Color, your text should be of.
After adding all the text, logo etc to your image, your certificate should look like the image below. When you are satisfied with the design of your certificate, save it as jpg image.