As there's been no reply to my post on this subject in general discussion, I'm adding to what I said there.

I'm very impressed with osclass but am a bit disappointed with how it deals with images.

If an item is listed with several images the first one is shown as the main ad display image and the others are shown in the margin. If you then click on one of the others it comes up in a black image box but you can't then scroll back to the previous image or forwards to the next one. You can go back but you can only do so by clicking the back button.

This isn't very elegant and I wonder if it would be possible to add a feature whereby when you click on an image, it opens in an overlay in which you can scroll through the available images before closing the overlay and returning to the ad itself.

You can see what I'm talking about in the French site Leboncoin.fr

not getting what is problem, I suppose it is related to how theme use image gallery ?

Does this vary by theme?

What I've described is what happens in Sigma.

What I'm looking for is an overlay that works like a slider with forward and back arrows. The overlay would open when you click on an image in the ad's image sidebar and would have an X in its top corner to close it again and return to the ad listing.

Ah, OK I get you. I've just looked and found what I need in the free 'Pop' theme except I hate everything else about the look and layout of Pop. What I'd like is to replace the product image display in Sigma with what appears to be called 'bxslider' in Pop. Any chance of that? I don't think I have the skills to do it but I'm going to have a go.

Ok got it.
Its default theme, will not co tain such fine tuning

OK I understand that.

But here's something weird. If you completely delete item.php from the Sigma theme the item still displays but in a different format that includes the site description strap line that's entered in the dashboard, which default Sigma does not, and also the image is displayed in a different way with a way to scroll through the item images in a slider overlay!

Can you explain that? Where's the image page then coming from?

Gui folder in oc-includes that simply act as last attempt to display page in acceptable format

Ah, maybe I'll be able to find the code that I need in there to change the standard item.php. Thanks for the info.

OK, I've found the relevant sections in each item.php - the standard oc content version refers to fancybox sigma gallery and the one I want to fancybox sigma group.

In fact the code in the 'includes' folder is from the bender theme so I referred to that.

However, when I paste the 'images' code from the bender version into sigma nothing changes - I still get the fancybox sigma version of images. I think that for some reason fancybox group is not working in sigma whereas it is in the bender theme.

What am I missing? Is it a js thing?

OK I get it now. Most (all?) themes DO HAVE an image scroll-through. It's just that it's broken in Sigma. So if like me you need that feature best not to waste your time with Sigma. I've now changed theme and am now much closer to getting a live web site after wasting days trying to get scrolling working in Sigma.

Back to work...

@RogSM
Each theme has different image gallery, that's it.
I am not aware it would be broken in Sigma theme as there is no scroll at all.

Yeah, not that it matters now as I've changed my theme, but the coding in the Sigma theme is all there as in eg Bender but it just doesn't work for reason(s) that I can't understand. I tried all sorts of things to make it work but don't have the php skills needed. Anyway, thanks for your help but as I say, I've moved on now and am very happy with the new theme that I'm now using.