GIMP is a free, open-source graphics editing program with a slew of features, similar to Photoshop and Paint Shop Pro. Like these proprietary graphics programs, it features filter effects that artistically alter the image. It has several options for making metallic images, but some of them are more intuitive than others.
Basic Metal Effects
The most basic way to make an image look more metallic is to use the Emboss filter. This filter makes the image appear as if it had been embossed onto a sheet of metal. The Emboss option is found under the Distort submenu of the Filters menu. In the Emboss window, drag the depth slider to "1" to make the image look cleaner, and ensure the bullet in front of "Emboss" is marked.
Alpha to Logo
The more complicated metallic effects are hidden in the Alpha to Logo submenu of the Filters menu. As the name suggests, they are intended to be used in the creation of logos. However, you can also apply them to ordinary images. Chrome is a simple metallic filter similar to Emboss. Cool Metal creates a shiny, sharp metallic image with a reflection and shadow, and adds a gradient to make the image look more reflective. Finally, Glossy makes the image look "shiny" and also adds a reflective gradient.
Using Alpha to Logo
In order to use the Alpha to Logo filters, you must first create an alpha layer. Press "Ctrl + A" to select the whole image, then go to "Colors" and select "Color to Alpha." Press "OK." From there, you can apply your filter of choice. For the Cool Metal and Glossy filters, pick a suitably metal-looking gradient to apply, such as "Brushed Aluminum" or "Cold Steel." Cool Metal creates multiple layers for the shadow and reflection. If you don't want these elements in your final picture, right-click the layer in the Layers panel and select "Delete."
Metallic effects work best on images with clearly defined lines, such as drawings. They can be used to "metallicize" photographs, but the results may not be as clear. Use the Sharpen filter, under the Enhance submenu, to make the edges more defined before applying the filter. If you want to make a colour drawing look more metallic without losing the colour, use the Glossy filter.