Let's say you catch someone using your images without permission...

... it's theft, plain and simple. They owe you money. Send them something like this...

Dear Sir/Madam,

With regards to your unauthorised reproduction of my
photograph - screenshot attached for your reference . As
I
am sure you are aware, no permission was sought for the usage, nor was any
compensation for its licence agreed between you and I, therefore you are in
breach of copyright.

As such, please consider this an invoice for
your
past usage of this image, as well as any further usage of this image as
part of
any reporting of this event in the future.

The invoice
breaks down as
follows.

Past and future usage of the image on : £make up a
figure of your choosing
Fee for unauthorised usage:
£insert the same figure,
as a penalty charge
Total: £the two figures
added up
In addition I also
require the image is credited to xxxxxxx

Payment is due no later than 30
days of the date of this email, and
should be paid via cheque made payable to
xxxxxxx at xxxxxxx.
Should
payment not be made within 30 days, the
unauthorised usage fee will double
to £double the unauthorised fee, and action
will be taken in the courts to
recover this sum, for which an additional fee of
£whatever you like will be
charged.

No further correspondance will be
entered into regarding
this matter.

Sincerely
Your name