This is really two questions, first, do browsers normally cache images on the client by default or does the server have to indicate that they can be cached? Second, given that I do not have access to IIS what can I do in an ASP application to improve client side caching of images.

Here is a useful link Are you generating the images yourself, or are they static files

Client side image caching with ASP.Net

This is really two questions, first, do browsers normally cache images on the client by default or does the server have to indicate that they can be cached?

Second, given that I do not have access to IIS what can I do in an ASP application to improve client side caching of images.

i haven't used this but you may be interested in taking a look at caching images in asp.net

A well-written browser will use the HTTP headers associated with the image to determine if the image should be cached and how long it should be cached for.

Take a look at the Cache-Control, Pragma, and Expires headers in the HTTP 1.1 specification.