According to Mike Chappell in Osprey British Battle Insignia, page 16 and plate section G4, the answer is...it depends on the regiment/brigade.
In mid-1917, the infantry of 23rd division consisted of 10 and 11 Northumberland Fusiliers, 12 and 13 Durham Light Infantry, 11 West Yorkshire, 8 and 9 Yorks (the Green Horwards), 10 Duke of Wellington's Own, 11 Nottinghamshire and Derbyshire (Sherwood Foresters), 8th Kings Own Yorkshire Light Infantry or KOYLI, 8 and 9 Yorks and Lancs and finally, 9 South Staffordshire pioneers.
23rd division battle patches were worn on the upper back of the uniform jacket. The 12th Durham Light Infantry wore a circle in a rectangle with a horizontal stripe through the middle. I think this would have been a yellow circle, red rectangle and darker red stripe, but I'm not certain. The brigade intermediate in seniority wore a slightly elongated red vertical diamond. The junior brigade, such as the 10th Duke of Wellington's wore either a silhouette of the regimental badge or a vertical device similar to their battalion number, for example an elongated 8 for the 8th Yorks and Lancs. Devices were also painted on helmets, such as the Duke of Wellington's red elephant with riding platform.
If nothing else, this should help you with researching the insignia on the web. I would pick a brigade/regiment and go from there. If you run into real difficulty, check out the Great War Forum web site. Ask there and I guarantee you'll get a quick and correct answer. Those guys and gals live, eat, & sleep insignia.
All the best,
Dan