At which point in KS3 are you planning to use this picture Stephen? I assume Y9 .. so given the work you do on 'portraits' unpacking this picture should be a doddle for your pupils
I know little about the picture other than that I have gleaned from a brief search on the www, but a number of points about the message it was
intendedto convey spring immediately to mind:
White people standing = superior
Black
king kneeling = inferior (but he's a
king!) Victoria giving present of Bible = a gift to be willingly accepted
Other white men standing but in background = not as important as Victoria
To me all this is pretty obvious so if I were using this in class I'd just give copies to small groups and get them to do one of those 'table top' exercises we've talked about on the Forum before. Or it might lend itself well to the creation of a 'tableau'/picture comic mentioned recently by Jo Norton. Even before you have done anything at all about the subject of Empire you could get your pupils to reenact the scene with each actor saying what they think might have been said by each person in the picture - or they could fill in speech bubbles on their group's copy (that could be also be done individually in ICT or collectively with interactive whiteboard).
The interesting thing that I have always found when dealing with propaganda is that for many youngsters (even quite old ones) propaganda is something used by the 'enemy' and not by 'us' so it will be good for them to analyse a picture which clearly has the intention of showing 'what good intentions we Brits had when we subjugated independent peoples' - for propaganda purposes. 'Cos this is a matter of convincing the British people that what we were doing was right - not the subjugated peoples.
All this could lead very nicely into work on the extent to which 'civilising heathen peoples' was the best explanation for British expansion -after an examination of other motives. When I have dealt with the Scramble for Africa (and in a Catholic school too) I have found most kids very cynical about the idea that Britain was primarily concerned to spread Christianity - but perhaps that's because the school has a highly international student body.