The new Google plus image size (as of 11/14/2013) has changed dramatically. There is more than one look and if you are using an image with text, it gets a little trickier.
On November 14, 2013 Google changed the new Google plus Image size once again. The day it happened, wanting to know the new size I Google'd "What is the New Google Plus Image Size" and all I found were older image sizes and templates, not the new one. I also found many conversations on LinkedIn and Facebook about whether we like the new one more than the previous one.
Regardless of whether we like it or not, it is what it is and if you are a company that has text in your Google+ Image, you may want to go check out your page and make sure it is viewing correctly.
Using the old Google+ image size Google+ will automatically change your old Google+ Image to the new size. This can change your header logo in several ways, but here are the two most common.
1) When Google+ adjusts your old dimensions of the Google+ image to the new, it can cut off the text.
2) When Google+ adjusts your old dimensions of the Google+ image to the new it will shrink the size of the text to where it is difficult or next to impossible to read.
To make it more challenging, Google Plus now has several different looks depending on how you land on the page. One is a Mobile version of the Google+ page and the other has a blurred left hand section with your company information overlayed.
This is even more important if you never adjusted it from original version of several years ago.
The New Google Plus Image Size
The New Google Plus image size is now similar to the new YouTube image size. You can work with anything in the aspect ration of 2560px wide by 1440px tall. So a 1280 x 720, 2120 x 1992 or a 480 x 270 or a 965 x 643 would work as well. (The image you upload to Google+ has to be at least 480 pixels wide and 270 pixels tall or it will not accept it.)
Not by coincidence I'm sure, it is also the same aspect ratio of a HD YouTube Video (1280 x 720).
The easiest fix to this is to simply use the same image you have for your new Youtube page, (Assuming you are using the new dimensions for your YouTube image). This will keep your branding the same and takes only a minute to change.
If you have not updated either your Google+ or your YouTube image, now is a good time to change it as it has never been easier now that the images are both the same size, any aspect ratio of 2560 x 1440.
Also, because your Google plus image will look different on a mobile, I suggest you put the text as near as center as you can. Below is a template you can use for the both new Google Plus Image Size and YouTube. Simply use these dimensions or alter the aspect ratio to fit your needs.