From Swftools

Swfrender creates bitmaps from swf files created with pdf2swf, jpeg2swf or png2swf.

Usage

   swfrender file.swf [-o output.png]

Options

Here are a quick summary of the available options for swfrender:

   -h , --help                    Print short help message and exit
   -l , --legacy                  Use old rendering framework
   -o , --output                  Output file (default: output.png)