Best picture size in Pixels ?

Hello Everyone!!!!

Quick Pixel Size question please. If you go to the Blog Link:
http://www.doceremedspa.com/blog

You will see the big Main Blog of course on the Left and the smaller mini EasyBlog Showcase on the right hand side column.

For any pictures IN the mini EasyBlog Showcase on the right to just show 1 Post (because as you can see in the Mini Blog their is the first Blue "Subborn Post" and then to the right is the White "24 Hour" second post) what is the correct Pixel size in Width and in Height that I need to have for ANY picture that I place into the main Blog so that when the EasyBlog Showcase on the right hand side pulls then they will be nice and even per Post IN the EasyBlog Showcase?

I would think their needs to be an ideal Width and in Height in Pixels that I can have for pictures in the main blog and I can resize these of course :-)

I just need to know the best Width and in Height in Pixels so when the EasyBlog Showcase pulls them they can be nice and even.

Thank You!!!

Byron Nemeth