Problem with metadata when sharing with Facebook

For two days ago something strange happened. I was going to share a blog post with my facebook friends and it was not before I posted the link that I saw there was a problem; The link to the post had been posted, but without any header photo. This has never been a problem before and I havent done anything new within my blog, so I have really no idea how to fix this. The strange thing is that when I paste the blog link into facebook’s comment field it shows the photo, and it is when I actually click post that the photo is gone. I tried several other posts from my blog, which I know have worked before, and the same thing happens to them. I have tried the Facebook debugger and it looks like there are some issues with the metadata, however, my knowledge on how to fix this is very limited.

For example one of the issues that the debugger points out is “og:image was not defined, could not be downloaded or was not big enough. Please define a chosen image using the og:image metatag, and use an image that’s at least 200x200px and is accessible from Facebook. Image ‘http://redisanattitude.com/wp-content/uploads/2015/12/the-best-hot-spring-in-japan_takaragawa-onsen-1200×797.jpg’ will be used instead. Consult http://developers.facebook.com/docs/sharing/webmasters/crawler for more troubleshooting tips.” –> my photos are always 1500 or 2000px, so this can’t be the problem.

Has anyone else experienced this, or maybe you have some suggestions on how I can fix this? Btw, this is the blog post I found the issue first on: http://redisanattitude.com/japan-takaragawa-onsen/