http://stackoverflow.com/questions/10048740/stop-browser-to-make-http-requests-for-images-that-should-stay-cached-mod-expi

http://stackoverflow.com/questions/15504550/check-if-image-is-in-cache-universal-image-loader

Thanks, Sanjay, I haven't seen these yet. I'll take a look and see if they have the answer I need.

Unfortunately, these links don't address my issue regarding persistent (unlimited) cacheing with Chrome running on Android. The first is code for some kind of extension called Universal Image Loader, the second is for a directive for an Apache server. Though this latter lead seems promising, I cannot find details of how I could use the "mod_expires" directives (or one like it) to specify long expiry dates for resources I specify in my cache manifest file. I have tried to find something along those lines that could tell the browser not to reload cache files ever, but have yet to find anything along these lines.

sorry for those links ....i am still trying to figure out best way for this and will update here.

Thanks, Sanjay.

Some clarification about the task (which is conducted from my project portal website at xvams.com): 

1) 7 pages of scales are presented random order, for which about 5MB of image files (101 per page) are required. The pages needing images are mixed in with pages that use simple, text based sliders which require no images.

2) After these have been submitted, there is a multiple choice questionnaire of 14 questions, each on a separate page.

3) There is then a REPEAT of 1), with the same pages and the same images being presented again (for the purposes of examining test-retest reliability).

In part 3, since the images were already downloaded in part 1, I would expect Chrome to go to the cache to re-use the images it already downloaded in part 1, but I see little or no evidence that it is even cacheing the files at all. Today I ran the experiment, and by the time my participant had reached 3), my router connection had slowed almost to a stop, and Chrome was struggling to reload the same images it had already loaded just a few minutes earlier. It is getting to the point where a 10-15 minute task is taking up to 50 minutes because of these unnecessary reloads. My participants are stroke survivors with varying impairments, and are easily fatigued by the long periods of tedious waiting involved.

I have ALL of these files on the tablet (Nexus 10 running Android 5.1) and there is absolutely no need for Chrome to download ANY of them more than once. All the resources are specified in the appcache file, and the Chrome console (Resources - Application Cache) confirms that it is downloading them as directed. Yet Chrome seems to totally ignore the cache and just goes back to a server half way across the world.

I have searched high and low on the internet for weeks now, and all I see are the same instructions for specifying the appcache file and how to include resources to use offline, but nothing seems to work at all, and even basic cacheing of my images in a single section seems totally absent (as shown by Chrome downloading the same images again in part 3). In total, there are 7 x 5MB = 35MB of images each, for 2 separate 'actors' modelling the images, - a total of 70MB that I want to just persist INDEFINITELY on my tablet, and for it to NEVER retrieve them again from online.

I would be really grateful if you or anybody else could help me figure this out, as it is killing my study. I just want cacheing to work the way it is supposed to, and for Chrome use offline resources without constantly downloading the same bandwidth-hogging images.