I have written an utility for it, its name is EasySpriteExtractor, just let me see how can I upload it because I'm new on romhacking.net and I don't know how to upload it.
Here is a screenshothttps://www83.zippyshare.com/v/buNh10jQ/file.html
And for now you can download it at:https://www83.zippyshare.com/v/dEpzIMdN/file.html
I leave you with the description of the software. I know it is not at all what you are looking for, but please tell me if this was useful for what you're trying to do.
Easy Sprite Editor (ese)
Is a simple tool with which as its name indicates,
sprites can be extracted from screenshots without
need to remove the background via emulator or other image edition
software. It is very useful when removing the background to
through the emulator the background color is the same as the color
of the sprite edges, which makes the extraction task very difficult.
It can be used through command lines (recommended).
To get more information about the commands, use /?
An example of how to use "ese" through command lines to extract the
sprites of multiple screenshots would be as follows:
ese.exe /ib "D:\Screenshots\SoM_BACK.png" /is "D:\Screenshots\SoM*.png" /x 108 /y 80 /w 24 /h 32 /e "D:\Export\export.png" /nogui
By using the / is (import sprite) command you can enter as many file names as you want, wildcards allowed (*).
If wildcards are used or more than one file is entered, using the /e (Export) command will add the file index between
the name and extension of each file successfully exported.
How it works?
It compares pixel by pixel on a specified area and outputs only unmatched pixels.