Best way to check would be to send it to a device over iMessage, saving it to the camera roll, then transferring it to a computer and checking the file size from the computer. Either use the cable to transfer it, Dropbox, or if AirDrop works then I guess use AirDrop. Don't use something like Imgur, this will compress the photo.
This is something
I've complained about in the past, iMessage doesn't compress photos/videos before sending them. This means you can get huge photos of like 3MB sent up and down, not only wasting storage space but also wasting mobile data and even iCloud storage.
I delete all of the pictures sent over iMessage (And my computer's iMessage will keep them so it's not like they're completely gone) but this is a bore. Luckily it seems you can nuke all the pics in a thread now but that doesn't solve wasting mobile data.
