geeky pics in high-resolution
legal: you can download high-resolutions images for non-commercial use only. in other words, you can use the pictures for making hand-out materials for conferences and meet-ups or decorating your walls at home or office, but you can't use the pictures for making money, i.e. put it on some objects and sell.
In agreement with /u/denholmsdead his images from linux related pictures project now are part of this project and can be distributed under the same rules.