Note: This tutorial was written for Inkscape, but should be applicable for other vector drawing programs with similar functionality.
Elvish Seer - Wesnoth Units Database
Mainline Campaigns - The Battle for Wesnoth Wiki
Goblin Warbanner - Wesnoth Units Database
Dwarvish Technocrat - Wesnoth Units Database
Mainline Campaigns - The Battle for Wesnoth Wiki
Lunatic Knight - Wesnoth Units Database
The Battle for Wesnoth — StrategyWiki Strategy guide and game reference wiki
Creating shadows under units - The Battle for Wesnoth Wiki
CastleTutorial - The Battle for Wesnoth Wiki
Portrait Tutorial - The Battle for Wesnoth Wiki
Mainline Campaigns - The Battle for Wesnoth Wiki
GitHub - wesnoth/wesnoth: An open source, turn-based strategy game with a high fantasy theme.
File:Wesnoth shield.svg - Wikimedia Commons
Variable-width strokes - The Battle for Wesnoth Wiki
MultiHexTutorial - The Battle for Wesnoth Wiki