Here is one I just did using a combination of MS Paint & Paint.net. I think it looks ok? I listed what I did below for anyone who wants to try for themselves. If anyone has any further advice. I'll take it.
Open up image in MS Paint:
Select - Free Form - Select All - Select Transparent Selection
Outline image then click crop (you don't have to be super exact) - Use eraser if necessary to remove any unwanted background - save as PNG file
Open Paint.net (free program)
Layers - Import from File - POE2 Background - ESC
Layers - Layer Properties - Blending Mode:Multiply
Image - Import From File - Select the cropped image - Adjust the image so it covers the background then - Layers - Layer Properties - Blending Mode:Multiply - ESC
From here you can use filters in the Adjustment\Effects to lighten the image\take sharper edges off etc...
I have primarily just used: Adjustments - Brightness\Contrast - Brightness to 40-50 or so to lighten up image and then contrast to 25-40, depending on the image
Effects - Blurs - Surface Blur - Often the standard Radius:6\Threshold 15 setttings are enough to soften up the image, otherwise I adjust the threshold from 10-25 depending.
There are all sorts of other things you can try, some of which I have messed around with. I just wanted something "fairly" quick and easy, and I have little\no expertise in these types of programs, but I think it works?
Once your done adjusting the image - ESC - Tool - Rectangle select - Select just the image\background area - Image - Crop to selection - then resize it if necessary - Image - resize - W:90 H:141 for convo & W:76 H:96 for si
File\Save - Make sure you save it as a PNG file