Error: I'm afraid this is the first I've heard of a "writeba" flavoured Blosxom. Try dropping the "/+writeba" bit from the end of the URL.
in case you were wondering
The smallest valid GIF image can be generated with the following command:
/usr/bin/printf
"GIF87a\x1\x0\x1\x0\x80\x0\x0\xff\xff\xff\xff\xff\xff\x2c\x0\x0\x0\x0\x1\x0\x1\x0\x0\x2\x2\x44\x1\x0\x3b"
Jim correctly points out that you don't actually need a color table. Moreover, only one byte of image data is actually necessary. Thus,
#/usr/bin/printf "GIF87a\x1\x0\x1\x0\x0\x0\x0\x2c\x0\x0\x0\x0\x1\x0\x1\x0\x0\x1\x1\x0\x0\x3b"