Rhiannon Harries: 'Nothing says 'Cheese!' louder than those online self-portraits'

You can spot them a mile off: the odd camera angle, a glimpse of awkwardly positioned arm. Mainly, it's the exaggerated tilt of the chin and the massive pout. No doubt the amateur photographic self-portrait pre-dates the social-networking revolution, but in the era of Facebook, MySpace, dating websites and Twitter, these über-posed images are everywhere.

In last week's furore around her alleged liaisons with footballer Wayne Rooney, reporters dug out some classic examples from Jennifer Thompson's Facebook albums. Since other pictures reveal Thompson to be the kind of gal who considers bra and knickers formal evening wear, you can hardly be surprised that at no point when creating such pictures did she stop to think, "Hmm, maybe this actually makes me look bit of a knob."

The try-hard self-portrait is not limited to wannabe Playboy bunnies, though. I've been taken aback several times by female acquaintances I'd thought were, you know, cool, popping up on screen apparently channelling Kate Moss. Ditto the odd male friend doing Ben Stiller in Zoolander. It seems perverse – if you are posing so outrageously that it's too shameful to ask another person to take the picture, why then share it with the world?

Of course, choosing a representative picture is tricky. It doesn't take an unhealthy level of vanity to prefer not to look an utter dog, so it is tempting to go for a flukey, ultra-flattering snap. But it opens up the possibility that people will a) not recognise you, creating an embarrassing "god is that you?" moment, and/or b) interpret your careful selection as a sign of pathetic vanity. Better to look like a dog, no?

I will admit that I have a default photo face (no-teeth smile, bite cheeks in a bit, try not to be caught shovelling food into gob). I plead that it's an attempt to look respectably average, not pro-model-pretty, and it doesn't always work.

For some, though, perhaps it is indeed a question of wanting to stack up to the beautiful people. So why, if the red-carpet pics in the glossies are anything to go by, do so many high-cheekboned, full-lipped celebs feel the need to pull the same moves?

Among the worst offenders are Liz Hurley, Sophie Dahl and Thandie Newton, none of whom need the help. Demi Moore's recent self-taken Twitter snaps of herself in a bikini (inset) were cringily unnecessary – she is known for little else than looking unfeasibly good these days; no need to overdo it. Still, I should be grateful – seeing a picture of Moore poncing it up probably does more for my self-esteem than one of Helena Christensen make-up free, mid-forkful and looking sublime.