Sorry it took so long to get to this.
There is s limit to the size of an image file that you can post - 3 megabytes is the ceiling, and a max of five files per post. It's to keep the storage requirements lower. The problem you run into, though, is that modern smartphones with built-in multi-megapixel cameras can create images that exceed this file size without much difficulty.
You can use simple image software to create a copy of your image file that's lower in resolution or smaller in size, thus reducing the size of the file. You can also try to lower the resolution of the image in the camera software when you're taking the picture, making it easier to post without an editing step.