However as an important rider to what Osiris has said - may I point out that, if you read the rules, what is NOT permitted is to post an image solely for the purpose of making a visual joke or snip, such as the Cat in the rules thread that Osiris posted - or indeed a rather amused horse that we had recently in another thread...
These images do not, of themselves violate forum TOS, however their use in that way IS against the guidlines to which Osiris has referred. Please be sure you understand this rule because many people seem to ignore it. Visual jokes like that should be confined to the humor sections and not posted in serious threads where they can seriously disrupt the flow.
In short if your point is a serious one then post away - but if you are simply using an image to say "I don't understand" or "You are talking rubbish" that would not be permitted even if the image itself was acceptable.
