I want to cache my jpg files

[#1]

PageSpeed /google is unhappy I'm not caching my jpg's and .css files.
I have used Sitemap to tell google about my normal htm files being are good for a day,(<changefreq>daily</changefreq>), how do I do the same for images & css?
What does plusnet support? Do I just put a file in htdocs ? Like htaccess ? to put a http header?
I just want them max-age=86400 e.g. a day.

[#2]

Try putting something like this into an .htaccess and upload it to your /htdocs folder:

ExpiresActive On
ExpiresByType image/jpg "access plus 1 day"
ExpiresByType image/jpeg "access plus 1 day"
ExpiresByType image/gif "access plus 1 day"
ExpiresByType image/png "access plus 1 day"
ExpiresByType text/css "access plus 1 day"

[#3]

Thanks bob
I now got this
Leverage browser caching
Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network.
Leverage browser caching for the following cacheable resources:
http://www.google-analytics.com/ga.js (2 hours)
http://www.shastonjazzandswing.co.uk/images/sjs_780x580.jpg (24 hours)
http://www.shastonjazzandswing.co.uk/pictures/pink_babs.jpg (24 hours)
http://www.shastonjazzandswing.co.uk/pictures/yellow_babs.jpg (24 hours)
http://www.shastonjazzandswing.co.uk/sjs_layout_mobile.css (24 hours)
http://www.shastonjazzandswing.co.uk/sjs_layout_monitor.css (24 hours)
http://www.shastonjazzandswing.co.uk/sjs_layout_printer.css (24 hours)
So it's seen the day part, but its still not happy, any ideas?

[#4]

Not sure TBH, something like this maybe?

[#5]

Do the messages simply mean a longer expiry time is recommended (eg 1 week or 1 month)?
David

[#6]

Thanks, looking again at PageSpeed I think you might be right.
Leverage Browser Caching
This rule triggers when PageSpeed Insights detects that the response from your server does not include caching headers or if the resources are specified to be cached for only a short time.
...
We recommend a minimum cache time of one week and preferably up to one year for static assets, or assets that change infrequently.
...

I changed .htaccess to
ExpiresByType image/jpg "access plus 1 week"
ExpiresByType image/jpeg "access plus 1 week"
to test this theory, it removed images from my list, it just complains about my css files.
Thank you both for your advice, I will tweak expires on css, when stable. Thanks again