To use your own picture as a post image or as a graphics object, feel free to upload it through the Uploads section. 

In the Graphics Editor, find Uploads on the left, then click the blue Upload button to bring an image from your computer to the platform. Such formats as .png, .jpg and .jpeg should be used. The file will appear on the artboard immediately after uploading. Now, you can simply drag and drop uploaded images to the Editor.

All the imported files will remain in your Upload section forever. And when you want to delete a certain image, just click on the bin sign.

Also, you can also organize your uploads according to the locations where you participate. Here is a detailed tutorial on that.