Replace ImageMagick thumbnail creating with GD Graphics Library aka libgd
Currently image thumbnails are created using shell outs to ImageMagick's convert tool.
There are multiple reason, why this might need to be changed. I do not want to list them here though, since they are largely fueled by FUD. Nevertheless, the latest ImageMagick security bug lead us to investigate alternatives to create thumbnails.
We came up with the following patch, which uses GD Graphics Library aka gdlib, gdlib2, or gdlib3.
- remove the newly introduced dependency to mimemagic, since there is no immediate need to verify the mime type of the image anymore.
- use the
local-fastimage_resizegem1 to perform the transformation.
- remove support for BMPs since libgd does not support them in all cases
Please note, that this will probably not work on Windows or JRuby, since interaction with libgd is done via its C API in a native c extension of the fastimage_resize gem.