Judging Size from a Photo......IMPOSSIBLE

This fish looks about 4 lbs., but it is
7 lbs. If you step back from the wide
angle lens and hold the fish close to
your body it appears smaller than it
really is.

This is the same fish that you see at
the right.  The photo was taken with
a wide angle lens and the fish is held
out to the camera. While it appears to
be about 15 lbs., it is really 7 lbs.
You simply can't guess the size of a
fish by the photo!

You see a lot of people posting photos of impressive carp these days all over social media.  Some of these fish look enormous, but we all know the biggest carp around here are maybe in the 40 lb. range. So, what makes a twenty pound carp look like a hundred pound tuna? Wide angle lenses.
Most high end smart phones have a standard lens and a wide angle lens. The wide angle lens allows you to get real close to the subject.  It spreads out the view, making any fish look much larger than it really is if you get up close.  If you hold the fish outward, it magnifies it even more.
Strange thing about the wide angle lens is that it can also make a fish look much smaller.  If you step back a bit from the camera and hold the fish close to your body, the fish can actually look smaller than what it is because the whole view is so spread out.
I don't object to fish looking bigger than what they are.  I sell a lot of photos and work for many magazines.  The wide angle shots are popular with editors and readers.  In addition, think about a photo in which the angler is holding a large fish.  The fish should be the central theme of the photo. In addition, these photos can generate a "wow" factor with people looking at them.
However, don't try to guess the weight of the fish by photos shot with wide angle lenses.  It's impossible.
Take a look at the two photos I've posted with this article. They are vastly different, but the same fish taken from different angles with a wide angle lens.