Pixel565 can be used to either create original artwork or import photos. The finished artwork can be converted to a block of rgb565 code. This is a series of hex codes which can be used with the arduino and the neopixel library. If you are using an esp8266 you can also send the image to the esp8266 over a WiFi connection.
This will only work if you have the necessary libraries and code installed on your arduino or esp8266.
Import photos to convert or use sprite sheets. Import the sprite sheet and crop it to the sprite you want to convert.