<s>
An	O
X-Face	B-Application
is	O
a	O
small	O
bitmap	O
(	O
48	O
×	O
48	O
pixels	O
,	O
black	O
and	O
white	O
)	O
image	O
which	O
is	O
added	O
to	O
a	O
Usenet	B-Application
posting	O
or	O
e-mail	O
message	O
,	O
typically	O
showing	O
a	O
picture	O
of	O
the	O
author	O
's	O
face	O
.	O
</s>
<s>
The	O
image	O
data	O
is	O
included	O
in	O
the	O
posting	O
as	O
encoded	O
text	O
,	O
and	O
attached	O
with	O
an	O
'	O
X-Face	B-Application
'	O
header	B-General_Concept
.	O
</s>
<s>
While	O
many	O
programs	O
support	O
X-Face	B-Application
,	O
most	O
of	O
them	O
are	O
free	B-Application
software	I-Application
and	O
based	O
on	O
Unix	B-Application
or	O
its	O
variations	O
,	O
such	O
as	O
KMail	O
or	O
Sylpheed	B-Language
.	O
</s>
<s>
The	O
most	O
common	O
email	O
programs	O
though	O
,	O
as	O
used	O
in	O
business	O
and	O
most	O
domestic	O
environments	O
,	O
do	O
not	O
handle	O
X-Face	B-Application
natively	O
,	O
and	O
the	O
information	O
is	O
silently	O
ignored	O
.	O
</s>
<s>
Even	O
where	O
Unix	B-Application
is	O
widely	O
used	O
(	O
university	O
and	O
research	O
environments	O
)	O
,	O
it	O
has	O
never	O
been	O
adopted	O
to	O
maximum	O
potential	O
(	O
for	O
example	O
,	O
by	O
searching	O
for	O
senders	O
by	O
X-Face	B-Application
)	O
.	O
</s>
<s>
A	O
further	O
development	O
is	O
the	O
Face	O
header	B-General_Concept
developed	O
in	O
2005	O
,	O
which	O
also	O
allows	O
for	O
color	O
images	O
in	O
PNG	O
format	O
,	O
and	O
can	O
be	O
used	O
by	O
the	O
Thunderbird	B-Application
addon	O
Display	O
Contact	O
Photo	O
,	O
as	O
well	O
as	O
some	O
other	O
mail	B-Operating_System
readers	O
.	O
</s>
<s>
Another	O
approach	O
to	O
include	O
the	O
sender	O
's	O
picture	O
in	O
an	O
e-mail	O
was	O
used	O
by	O
Apple	O
:	O
Mail	B-Operating_System
displayed	O
the	O
picture	O
if	O
the	O
mail	B-Operating_System
included	O
the	O
X-Image-URL	O
header	B-General_Concept
.	O
</s>
<s>
In	O
1992	O
,	O
this	O
feature	O
was	O
originally	O
implemented	O
in	O
NeXTmail	O
,	O
Mail.app	B-Operating_System
'	O
s	O
ancestor	O
.	O
</s>
<s>
As	O
of	O
Mail	B-Operating_System
v4.5	O
,	O
the	O
feature	O
is	O
no	O
longer	O
supported	O
.	O
</s>
