File `neboltai.png` is actually a JPG file.

A `file src/neboltai.png` reveals that this file is actually a JPG file:

    $ file src/neboltai.png
    neboltai.png: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 1596x2225, frames 3

Changed extension accordingly.