Flask extension, failing to return image path when using sub-path of root - flask

Question

I'm working on adding additional functionality to Flask-Resize, specifically adding a feature that should serve the original file instead of generating a cached file if the size and other parameters are the same as the original.
I have everything worked out in the checks and so forth, and everything works fine if the image is in the RESIZE_ROOT directory but if not, when the image generator detects that it doesn't need to do anything and returns the original file path, jinja2 doesn't seem to fetch the image.
Using an image test_img.jpg with a size of 200x300px, in the RESIZE_ROOT directory works fine:
<img src="{{ 'test_img.jpg'|resize('200') }}"></img>
Output:
http://127.0.0.1:5000/static/images/test_img.jpg
127.0.0.1 - - [23/Oct/2015 03:44:28] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [23/Oct/2015 03:44:28] "GET /static/css/main.css HTTP/1.1" 200 -
127.0.0.1 - - [23/Oct/2015 03:44:28] "GET /static/images/test_img.jpg HTTP/1.1" 200 -
-- test_img.jpg fetched and displayed correctly
However when the image is moved to a sub-directory say ad/test_img.jpg, then the console output doesn't even indicate that it is fetching the image
http://127.0.0.1:5000/static/images/ad/test_img.jpg
127.0.0.1 - - [23/Oct/2015 03:58:42] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [23/Oct/2015 03:58:42] "GET /static/css/main.css HTTP/1.1" 200 -
-- ad/test_img.jpg isn't even being fetched
Putting image generates a valid link to the image, so the file path is getting returned correctly so I have no idea what's going on.
This is the relevant code; generate_image raises a exc.StopImageGeneration exception if it detects that it should not generate an image.
if not os.path.exists(full_cache_path):
try:
generate_image(inpath=original_path, outpath=full_cache_path,
format=format, width=width, height=height,
bgcolor=bgcolor, upscale=upscale, fill=fill,
anchor=anchor, quality=quality,
progressive=progressive,
placeholder_reason=placeholder_reason,
force_cache=force_cache)
except exc.StopImageGeneration:
full_cache_url = unicode(resize_url+image_url)
print (full_cache_url)
return full_cache_url.replace('\\', '/')
And my Flask-Resize initialisation parameters if it matters:
(RESIZE_URL='http://127.0.0.1:5000/static/images/', RESIZE_ROOT='static/images/')

Answer 1

So turns out this has nothing to do with Flask/Jinja2, it's Adblock's fault; it was blocking the images silently.
After I added an exception for localhost and 127.0.0.1 there was no problem.