Regardless of what kind of digital spacecraft image you want to make, you can likely make it in GIMP--The GNU Image Manipulation Program, a free alternative to Adobe Photoshop. You can use the advanced editor to design intricate spaceships using various textures, backgrounds and modes of lighting--maintaining images on separate layers giving you maximum control when customising and creating. Using GIMP, you can insert pre-made graphics to build around or you can start entirely from scratch: the approach is up to you.
Open the graphics editor and click "File" and "New." Select the image size of your choice along with X and Y resolutions of at least 100 pixels per inch for an optimal view. If you want to make a spaceship with a transparent background, you may want to choose "Transparency" as the "Fill with" option; otherwise, you can let the default setting be.
Select "Layer" and "New Layer" with "Fill Type" as "Transparency" to insert a new layer. Click on the "Blend Tool" and select a gradient type to create a multifaceted background for your spaceship; consider using a style such as "Deep Sea" or "Polluted Sky." Click on one corner of the workbook and drag your cursor to the other to implement the effect.
Insert another layer and use the "Paintbrush Tool" on this top layer to design the basic outline of your spacecraft. Continue using the paintbrush to fill in the shape, or use the "Bucket Fill Tool" with the "FG Color Fill" option selected.
Click on the "Bucket Fill Tool" with "Pattern Fill" highlighted to select a texture to give to your spaceship. Consider using the "Slate," "Recessed" or "Paper" fill for the base of your spacecraft, and click on the ship once you have selected the texture.
Add a shadow to your spaceship by clicking on "Filters," "Light and Shadow" and "Drop Shadow," pressing "OK" after the pop-up box appears.
Insert a new layer and select "Filters" then "Light and Shadow" and "Gradient Flare," choosing effects such as the insertion of "Bright_Star" or "Hidden_Planet." Repeat, as desired, to add more interest to the background scenery.
If the "Layers" toolbar is not visible, you can click on "Windows" and "Dockable Dialogs" to then select "Layers."
To save your workbook as a multilayered, easy-to-edit format, use GIMP's native file extension ".xcf" in addition to saving your final product as a picture file with a picture extension such as ".jpg" or ".png."