open graph images - best dimensions for linkedin/ facebook etc. ?

i am nearly finished with the social sharing plugin for elgg that i am coding.

one of the remaining issues to be fixed is to ensure that the metatag for open graph images is inserted in a way that the recipient sites can use. this though, is not as simple as i imagined.

facebook provides a debugging page for opengraph data here:
https://developers.facebook.com/tools/debug/og/object?q=https%3A%2F%2Fwww.infiniteeureka.com%2F

as you can see that the debugging data for my site's homepage says:

Provided og:image is not big enough. Please use an image that's at least 200x200 px.

except that the image i am using IS larger than 200x200.

then, when i looked at linkedin's advice page for this issue here: https://developer.linkedin.com/documents/setting-display-tags-shares

they say that: LinkedIn Today requires images to be at least 80 x 150 pixels.

Note: Facebook also uses Open Graph tags, but does not require og:image sizes as large as LinkedIn. If you use the image size required by LinkedIn Today, the image is scaled down to work for Facebook.

Tips: A few suggestions that'll help with the image quality. When presented in the feed, the image, regardless of what you've uploaded is always sized 180x110. Our algorithm crops the image too. So, the original image -

  • Should be smaller than 180x110

so there is contradiction here.

i am unclear on how to correctly size the images.

in addition to this - i discovered that we need to use a seperate image tag if our site is an https site:

http://ogp.me/#structured

og:image:secure_url is to be used in place of og:image

so.. i did that.. and still my chosen images are being rejected and not used by google+ and facebook.. the only error message i have seen is the facebook debug page message about the image size. so.. 
anyone know how to resolve this?

thanks