Hi James,
First your French case, the EU decision of Pez Hejduk. v. EnergieAgentur.NRW GmbH says in layman's terms that if an infringing image is visible on an EU website in one country, you can take action in that country regardless of where the defendant is based. Having said that, as Andy J pointed out, you would need to have the judgement enforced in France and you can expect the whole process to be difficult and complicated.
With regards to damages in your UK claim this is straight forward. If you are a practising professional photographer with a track record of sales, then you should present evidence of this and your normal sales price will almost certainly be accepted by the court as the base value of the work. If on the other had, you do not normally licence photographs then the court will consider market rates. You will no doubt as claimant present evidence of expensive photos while your opponent will present evidence of cheaper photos with the court left to decide which is applicable.
Suitable case law to read would be
Irvine & Ors v Talksport Ltd [2003] EWCA Civ 423
http://www.bailii.org/cgi-bin/format.cg ... tml&query=(title:(+Irvine+))+AND+(title:(+Talksport+))
This case shows that what is relevant is your own prices rather than the prices others charge.
Jason Sheldon v Daybrook House Promotions Ltd [2013] EWPCC 26
http://www.bailii.org/cgi-bin/format.cg ... tml&query=(title:(+sheldon+))+AND+(title:(+daybrook+))+AND+(title:(+house+))
As above but in a photograph context.
One of the most important judgements to read is Absolute Lofts South West London Ltd vs Artisan Home Improvements Ltd & Darren Mark Ludbrook [2015] EWHC 2608 (IPEC)
http://www.bailii.org/ew/cases/EWHC/IPEC/2015/2608.html
This case shows the courts methodology in the case of a collection of amateur photographs which had not been offered for sale. The case also outlines the courts approach for "additional damages". In this case the court valued the infringed photographs at £300 but the awarded additional damages of £6000 on top. The Courts can award additional damages either for flagrancy pursuant to section 97(2) Copyright Designs and Patents Act 1988
https://www.legislation.gov.uk/ukpga/1988/48/section/97 or alternatively in order to dissuade this infringer and other potential infringers from infringing pursuant to Directive 2000/31/EC of the European Parliament and of the Council of 8 June 2000 on certain legal aspects of information society services, in particular electronic commerce, in the Internal Market ('Directive on electronic commerce')
http://eur-lex.europa.eu/legal-content/ ... 32000L0031
NB If there is any conflict between the EU Directive and the UK Act then the EU directive takes precedence. Interestingly I Absolute lofts, the court chickened out of deciding whether the damages should be for flagrancy or dissuasion and decided that they would have awarded the same under either legislation.
The absolute lofts case was at the upper end of what the courts award for additional damages. In the cases I am aware of in the small claims track, typical amounts range from 2x to 6x the normal value of work depending on the facts of the case.
When issuing your claim you must make clear on what legal basis you claim additional damages, so do quote section 97(2) and the EU directive above. As for the amount of additional damages, well you can either ask the court to consider an amount, or you can leave it completely up to the court ie " I claim an amount pursuant to section 97(2) to be decided by the court".Either way the sum is up to the court to decide. In practical terms and for the purpose of negotiating a settlement then its probably best to decide a reasonable sum the court may award and base your claim on that. Thus if you normally charge 500 GBP to use a photograph and the defendant has behaved very badly ( eg commercial use / big company / big use / removed name / removed meta data ) you may decide to claim 2000 GBP, ie 4x your normal price. You can always accept a lower offer. Just be aware of the risks of turning down a reasonable offer. If in the above case you turn down an offer from the defendant of say 1000 GBP because you are holding out for 1500 gbp and then in court the judge awards 8000 GBP then in all likelihood the court will make you pay the defendants costs. Costs are very limited in the small claims track so you may consider this risk worth taking but its wise to be reasonably flexible.
As for the practicalities of issuing a claim, you need to read the links Andy J sent ( don't issue a claim without reading them!! ) Also a nice step by step guide in layman's terms can be found on the Editorial Photographers UK website at
http://www.epuk.org/the-curve/the-infri ... ight-claim. It includes some sample Letters of Claim and relevant links. It might look a bit complicated at first but don't worry, its straight forward as you work through it step by step. Very many photographers are now enforcing their rights through the IPEC small clams track.