Here is the tutorial on how to make UNDETECTED texture (skin/camo/scope/...) modifications. Tutorial can help you making all kind of texture modifications not only skins as shown in tutorial.
House - making Tutorial
THT - Archangel, Seba & me - Idea
SuperNovaAO - CRCFix
Download TOOLS.rar and extract it on your desktop.
- Iwi x Dds (convert the .iwi files to a .dds format, which can be opened in photoshop with the plugin provided)
- dds2iwi (use this to convert your file back to an .iwi file, so it can be used ingame)
- HxD editor (a hex editor)
- CRC32Fixer (use this to make the files work in public matches)
- Photoshop Plugin (to open and edit .dds files in photoshop)
Download Photoshop here
Follow the tutorial in images and make your custom textures.