1) is there a vacuum exhauster on the right side?
1a) if so, identify side panels
2) is there an air brake compressor cabinet on the left side?
3) bonnet doors - riveted or pressed steel?
4) type of bonnet front grilles, and whether lower cover present
5) position of front and rear marker lights
6) whether ladders around front bonnet (early locos)
7) wooden or pressed cab doors
Not being a photographer, I haven't got any locomotive photos of my own, but fortunately these days many people are happy to share their collections on the web.
I'm looking for photos of locos as they were at the time - showing clearly all livery details, and of course the grime that I'll need to represent. So Preservation Society sites don't count. To my mind, these locos don't look right if they're kept too clean.
some useful sites
I found Rail Photo Archive a good place to start. It's the most comprehensive of the ones I know, and you can search for your favoured time, livery or location.
There are also photographs of a large number of locos (and some related stuff - he appears to be an ex-worker at Cardiff Canton depot) on Martin Bray's site. In particular his 08 / 09 gallery includes a photo of many 08's, together with date and place taken, from the 70's onwards.
Graham Turner's Rail Blue site has additional information on many of the photographs, dated around the 70's to early 80's.
Colin Marsden's books are mentioned in the instructions. He also has a website therailwaycentre.com with some technical information.
Mark Shipman has a section on 08s from the 80's onwards.
Comparing these photographs against my Motive Power Pocket Book (1992) suggests that the air brake compressor cabinet is present on the left side for locos with dual (air and vacuum) brakes, but not for those with air brakes only.
Railfaneurope has a gallery of shunter pictures from various contributors, mostly from the 90's onwards.
Dazza has 08s from the 90's onward.
Justin Buckley, Dave Swan and The Bufferstops all have small selections of recent 08 pictures.
Robert McCulloch has some Scottish-based photos.
Colin Birch has 08 and 09 sections, unfortunately not all the photographs are dated.
Andy Small has some nice photographs of 08s at work "in the landscape" but by their nature they're not the best to establish detail.
Locoscene takes some time to browse, but if you know what you're looking for just log in as "guest" then type the loco number in the "find loco" box.
Far from having no photos to model from, now I'm spoilt for choice. Eventually decide to go for 08801 as I found several clear images from the 80's, but also because they were taken around Penzance in Cornwall. I once spent a happy afternoon there around 1971 just watching the trains from behind the wall, thinking grand thoughts about modelling the station. This could be my first small step towards that dream...