Hello!
WP-Portfolio does not currently support “Custom Sizes”, “Full-Length”, or “Custom Viewport (browser resolution)”.
However, we are currently working on a major overhaul that will add quite a few new features, including all of those. So, if you can hold out for 1-2 months, the new version should be MUCH more powerful. Please note, though, that “Custom Sizes” require an upgraded account with ShrinkTheWeb, if you plan to use the automated screenshot service.
If you are planning to upload your own images or cannot wait for the new release, then you “could” (not recommended to hack core, though) modify the plugin to get a custom size. I’ve never made that modification before and could easily spot where to do it just now, but I know that others have reportedly done it.
I will check through the forum to see if anyone has posted their steps OR dig deeper in the code to point out where you would make that change, should you feel so inclined. ??
Best regards,
Brandon