Here are my own thoughts on this, others will have other thoughts and suggestions:
I think this a an excellent idea but I would start by adding a proviso - it is important imo to learn to identify birds in the field as well as from photos - otherwise you are relying on a photo being clear and unambiguous which we know from ID threads, is not always a luxury afforded to us, so may miss out on being able to ‘tick’ the bird you actually saw which would be a shame.
While excellent digital images have been a game changer for identifying confusion species, it can’t replace real live experience in my humble opinion. I find that establishing a bird’s identity in the field is more often than not, more than just plumage consideration but also a combination of behaviour, habitat, vocals, body shape, flight pattern and size comparisons. All of which are in some way obscured in photo-imagery due to being reduced to a 2-dimensional stilled format even in the best of images. For example, Forsman’s photographic guide to Flight Identification of Raptors is one of the best examples of how digital photography can help us learn but even that is not a replacement for field experience. More often than not, for those of us who are not very competent photographers, when we get home and look at our photographic efforts, only part of the bird is visible in a shot or the photo simply isn’t good enough to see all the important features clearly to be barely any use to identify the species let alone good enough for an online teaching aid..
Having said that, I think you have a great idea but for copy right reasons, it would need the permission of the photographer to upload images here, so you would have to rely on members own images. I don’t have any personally that would be much help otherwise I would be more than glad too - most of my old birding images are stored on CDs and I no longer have the means to upload them. . I expect there will be someone though who is willing to talk you through their images.
This site may be helpful
https://www.birdid.no/bird/eBook.php?specieID=1490&compareSpecieID=1886
In the meantime I would just add getting more field experience of even just Common Whitethroats so you can know enough to know when the sylviid flitting around in the shrubs in front of you isn't one!
It would also be of great benefit to find a local more experienced birder who can take you to reliable site for Spectacled Warbler and point out the salient identifying criteria while you watch the bird.
I also would suggest to watch loads of videos if you can (as well as looking at online images) as video’s teach you about movement and jizz and flight style which you will help you recognise a species a lot quicker if you come across it in the field.
Also familiarise yourself with calls and songs, especially helpful for sylviids lurking in bushes. I have the Sunbird app ‘Bird Songs of Europe’ which is excellent, has sonagrams of every call and song on the app and for most species it has songs, subsongs, calls and fledgling calls
https://play.google.com/store/apps/details?id=com.sunbirdimages.birdsongseurope&gl=GB
You will often find videos on youtube or twitter or birding news sites.
http://www.rarebirdalert.co.uk/v2/C...ham_Overy_Norfolk_Jun_2014.aspx?s_id=62585133