Usually the images come in whatever the designer name it and most of the time Android SDK don't like this naming, this is NodeJS script that fixes the filenames for Android PNG.

fixAndroidResourcesFilenames.js

#!/usr/local/bin/node

var fs = require("fs");
var filenames = fs.readdirSync(".");

var a = "a".charCodeAt(0);
var z = "z".charCodeAt(0);
var c0 = "0".charCodeAt(0);
var c9 = "9".charCodeAt(0);
var acceptableChars = {"_":true,".":true}

var bA = "A".charCodeAt(0);
var bZ = "Z".charCodeAt(0);

function between(target,from,to){
	if(target>=from && target<=to)
		return true;
	return false;
}


var currentPath = fs.realpathSync(".").split("/");
if(currentPath<=0)
	process.exit()

if(currentPath[currentPath.length-1].indexOf("drawable")+8 >= currentPath[currentPath.length-1].indexOf("dpi")){
	console.log("The folder doesn't seem to be Android resource folder.")
	process.exit()
}

for (var filenameIdx in filenames){
	var isLastIsUnderscore = false;
	var newName = "";
	
	for(var charIdx in filenames[filenameIdx]){
		var currentChar = filenames[filenameIdx].charCodeAt(charIdx);
		if( between(currentChar, a, z) || 
			between(currentChar, c0, c9) || 
			acceptableChars[filenames[filenameIdx][charIdx]]){
			
			newName += filenames[filenameIdx][charIdx];
			isLastIsUnderscore = false;
		}else{
			if(!isLastIsUnderscore){
				if(between(currentChar, bA, bZ)){
					if(newName.length==0){
						newName += filenames[filenameIdx][charIdx].toLowerCase();
					}else{
						newName += "_" + filenames[filenameIdx][charIdx].toLowerCase();
						isLastIsUnderscore = true;
					}
				}else{
					newName += "_";
					isLastIsUnderscore = true;
				}
			}else{
				if(between(currentChar, bA, bZ)){
					newName += filenames[filenameIdx][charIdx].toLowerCase();
				}
			}
		}
	}
	fs.renameSync("./" + filenames[filenameIdx], "./" + newName);
}

console.log("Filenames fixed")