Hi, I am no expert by any means but here is what I think. When I click on properties to post I look at the dimensions part and if it is around 400x pixels I know it is a reasonable size to post. For example if you look at the picture of puppy Bob I posted in "Zeke update" thread that is 400x352 pixels. Check out some of the other pictures posted on Pet Talk for the pixel size ( right click then click properties) and you will be able to see the difference in pixel sizes. Hope this helps.