Featured Images Are Becoming Stretched

Try making you image 1038 bytes wide – I am not sure the height matters but it might do – I think you have to play around with it
I used an image 1037 × 296
This is not a very clever solution but it worked for me

Sorry for the delay in getting back to you.
I have tried that just now and it made no difference.
If I dont use the “content sidebar” widget it seems fine, but I want to use that widget.

hi,
themes can set a specific size for the thumbnail image and TwentyFourteen sets is to: width 672 pixels, height 372 pixels, with the “crop” parameter set to “true”.
That means it will try to resize *and* crop the thumbnail images to that exact size.
Keep in mind WordPress can’t *upscale* images, but just downsize them.
Now, your original image is 2374 x 897 pixels, bigger than the thumbnail size so WordPress is able to resize and crop it to exactly 672×372.
You have 2 options:

1)
start from an original image with same ratio or multiple of 672×372, for example: 1344×744 and so on and for doing this you will have to add “white space” on top and bottom of your image.

or:

2)
start from an image with an height less than 372 pixels. The interesting part here is WordPress can’t upscale images so, for example, if you start with an image of 800×302 WordPress will be able to reduce the width but it won’t increase the height. The result will be a thumbnail image of 672×302.
I fear also in this case you will need to add a bit of “white space” on top and bottom of your original image because its ratio is very “stretched” horizontally compared to the thumbnail ratio (672×372)