An application to the FMS may be rejected in cases where the passport goes beyond the image or highlights are present.
Check the validity of your passport:
You won't get a visa if it is valid for less than 6 month after the alleged departure from Russia.
If there are no blank pages or the validity ends, you'd better issue a new passport
There are no restrictions on the file size, however, keep in mind that an image captured by a modern cellphone is quite large, so it may require some time to upload it after clicking the "send" button. Meanwhile, do not rush to refresh the page - wait until the message will appear, indicating the result of action. In case if something went wrong - you will see the revelant message and you'll be redirected on the same page again.