<s>
Error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
(	O
ELA	O
)	O
is	O
the	O
analysis	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
in	O
digital	O
data	O
with	O
lossy	B-Algorithm
compression	I-Algorithm
such	O
as	O
JPEG	O
.	O
</s>
<s>
When	O
used	O
,	O
lossy	B-Algorithm
compression	I-Algorithm
is	O
normally	O
applied	O
uniformly	O
to	O
a	O
set	O
of	O
data	O
,	O
such	O
as	O
an	O
image	O
,	O
resulting	O
in	O
a	O
uniform	O
level	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
.	O
</s>
<s>
Alternatively	O
,	O
the	O
data	O
may	O
consist	O
of	O
parts	O
with	O
different	O
levels	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
.	O
</s>
<s>
This	O
difference	O
may	O
arise	O
from	O
the	O
different	O
parts	O
having	O
been	O
repeatedly	O
subjected	O
to	O
the	O
same	O
lossy	B-Algorithm
compression	I-Algorithm
a	O
different	O
number	O
of	O
times	O
,	O
or	O
the	O
different	O
parts	O
having	O
been	O
subjected	O
to	O
different	O
kinds	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
A	O
difference	O
in	O
the	O
level	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
in	O
different	O
parts	O
of	O
the	O
data	O
may	O
therefore	O
indicate	O
that	O
the	O
data	O
has	O
been	O
edited	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
JPEG	O
,	O
even	O
a	O
composite	O
with	O
parts	O
subjected	O
to	O
matching	O
compressions	O
will	O
have	O
a	O
difference	O
in	O
the	O
compression	B-Algorithm
artifacts	I-Algorithm
.	O
</s>
<s>
In	O
order	O
to	O
make	O
the	O
typically	O
faint	O
compression	B-Algorithm
artifacts	I-Algorithm
more	O
readily	O
visible	O
,	O
the	O
data	O
to	O
be	O
analyzed	O
is	O
subjected	O
to	O
an	O
additional	O
round	O
of	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
this	O
time	O
at	O
a	O
known	O
,	O
uniform	O
level	O
,	O
and	O
the	O
result	O
is	O
subtracted	O
from	O
the	O
original	O
data	O
under	O
investigation	O
.	O
</s>
<s>
The	O
resulting	O
difference	O
image	O
is	O
then	O
inspected	O
manually	O
for	O
any	O
variation	O
in	O
the	O
level	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
.	O
</s>
<s>
In	O
2007	O
,	O
N	O
.	O
Krawetz	O
denoted	O
this	O
method	O
"	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
"	O
.	O
</s>
<s>
Additionally	O
,	O
digital	O
data	O
formats	O
such	O
as	O
JPEG	O
sometimes	O
include	O
metadata	O
describing	O
the	O
specific	O
lossy	B-Algorithm
compression	I-Algorithm
used	O
.	O
</s>
<s>
If	O
in	O
such	O
data	O
the	O
observed	O
compression	B-Algorithm
artifacts	I-Algorithm
differ	O
from	O
those	O
expected	O
from	O
the	O
given	O
metadata	O
description	O
,	O
then	O
the	O
metadata	O
may	O
not	O
describe	O
the	O
actual	O
compressed	O
data	O
,	O
and	O
thus	O
indicate	O
that	O
the	O
data	O
have	O
been	O
edited	O
.	O
</s>
<s>
By	O
its	O
nature	O
,	O
data	O
without	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
such	O
as	O
a	O
PNG	O
image	O
,	O
cannot	O
be	O
subjected	O
to	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
.	O
</s>
<s>
Consequently	O
,	O
since	O
editing	O
could	O
have	O
been	O
performed	O
on	O
data	O
without	O
lossy	B-Algorithm
compression	I-Algorithm
with	O
lossy	B-Algorithm
compression	I-Algorithm
applied	O
uniformly	O
to	O
the	O
edited	O
,	O
composite	O
data	O
,	O
the	O
presence	O
of	O
a	O
uniform	O
level	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
does	O
not	O
rule	O
out	O
editing	O
of	O
the	O
data	O
.	O
</s>
<s>
Additionally	O
,	O
any	O
non-uniform	O
compression	B-Algorithm
artifacts	I-Algorithm
in	O
a	O
composite	O
may	O
be	O
removed	O
by	O
subjecting	O
the	O
composite	O
to	O
repeated	O
,	O
uniform	O
lossy	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Also	O
,	O
if	O
the	O
image	O
color	O
space	O
is	O
reduced	O
to	O
256	O
colors	O
or	O
less	O
,	O
for	O
example	O
,	O
by	O
conversion	O
to	O
GIF	O
,	O
then	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
will	O
generate	O
useless	O
results	O
.	O
</s>
<s>
More	O
significant	O
,	O
the	O
actual	O
interpretation	O
of	O
the	O
level	O
of	O
compression	B-Algorithm
artifacts	I-Algorithm
in	O
a	O
given	O
segment	O
of	O
the	O
data	O
is	O
subjective	O
,	O
and	O
the	O
determination	O
of	O
whether	O
editing	O
has	O
occurred	O
is	O
therefore	O
not	O
robust	O
.	O
</s>
<s>
In	O
May	O
2013	O
,	O
Dr	O
Neal	O
Krawetz	O
used	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
on	O
the	O
2012	O
World	O
Press	O
Photo	O
of	O
the	O
Year	O
and	O
concluded	O
on	O
his	O
Hacker	O
Factor	O
blog	O
that	O
it	O
was	O
"	O
a	O
composite	O
"	O
with	O
modifications	O
that	O
"	O
fail	O
to	O
adhere	O
to	O
the	O
acceptable	O
journalism	O
standards	O
used	O
by	O
Reuters	O
,	O
Associated	O
Press	O
,	O
Getty	O
Images	O
,	O
National	O
Press	O
Photographer	O
's	O
Association	O
,	O
and	O
other	O
media	O
outlets	O
"	O
.	O
</s>
<s>
Hany	O
Farid	O
,	O
said	O
about	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
that	O
"	O
It	O
incorrectly	O
labels	O
altered	O
images	O
as	O
original	O
and	O
incorrectly	O
labels	O
original	O
images	O
as	O
altered	O
with	O
the	O
same	O
likelihood	O
"	O
.	O
</s>
<s>
In	O
May	O
2015	O
,	O
the	O
citizen	O
journalism	O
team	O
Bellingcat	O
wrote	O
that	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
revealed	O
that	O
the	O
Russian	O
Ministry	O
of	O
Defense	O
had	O
edited	O
satellite	O
images	O
related	O
to	O
the	O
Malaysia	O
Airlines	O
Flight	O
17	O
disaster	O
.	O
</s>
<s>
In	O
a	O
reaction	O
to	O
this	O
,	O
image	O
forensics	O
expert	O
Jens	O
Kriese	O
said	O
about	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
:	O
"	O
The	O
method	O
is	O
subjective	O
and	O
not	O
based	O
entirely	O
on	O
science	O
"	O
,	O
and	O
that	O
it	O
is	O
"	O
a	O
method	O
used	O
by	O
hobbyists	O
"	O
.	O
</s>
<s>
On	O
his	O
Hacker	O
Factor	O
Blog	O
,	O
the	O
inventor	O
of	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
Neal	O
Krawetz	O
criticized	O
both	O
Bellingcat	O
's	O
use	O
of	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
as	O
"	O
misinterpreting	O
the	O
results	O
"	O
but	O
also	O
on	O
several	O
points	O
Jens	O
Kriese	O
's	O
"	O
ignorance	O
"	O
regarding	O
error	B-General_Concept
level	I-General_Concept
analysis	I-General_Concept
.	O
</s>
