Pixelation issue

[Dogtaggart]

Hi all
Wonder if someone can help. A while ago I posted a few shots as a newbie, they were not that great hence the title "starting somewhere".
I was just going through my pc's picture files and pulled up one of them - when I opened it I found it has pixelated, checked the other 2 and they were the same.
So I looked up the pics on my post here and again all pixelated but I know they weren't like that when I first saved them
I hope this doesn't sound like I'm trying to make excuses for poor pics, I'm not - just wonder what I did wrong to make them go like this??? I had to reduce the file size in order to post, would that have something to do with it?
Just want to avoid making the same error again in the future!
Attached one here to show, sorry it's only a thumbnail so might be hard to see, haven't sussed out flickr yet...
Is there any way I can undo this?

We need more details than just this.

Oversharpened? Too small of a image? Saving properties?

All could be the answer.

[Dogtaggart]

each had small amount of PP in Gimp but I don't believe oversharpened. They were all ok when I viewed them on my PC until I reduced the size of the jpeg (in Windows picture manager) in order to post on here.
The one I show here I actually saved to my desktop before posting and that is still ok on my opening screen.
I run Vista...

you probably saved them too "small" and by that i mean the saving properties you used were not enough and compressed too much.

[Dogtaggart]

that sounds like it - I reduced the size using Windows picture manager to fit web pages, What is the best way to do it - get to grips with Flickr? excuse my obvious ignorance!
Thanks for the feeback will have to try again with another but leave it a bit bigger and see if that's ok.