I am running a picture blog and am using adsense for advertising. The problem is that adsense keeps showing house ads mostly. I am assuming that this is because there is limited amounts of actual text. Any suggestions on how I can improve this?

Add some text.

Add text with pictures of different format that would be related to natural objects etc

Make sure your images (pics) have keyword related "ALT" text.

My personal opinion is that you would be better off finding some affiliate products or services that are related to your content and integrating them throughout your site.

You need a LOT of traffic to see any return from Adsense and most people have become "blind" to Adsense ads.

Think about it. How often do you click on Adsense ads?

I tried adding a caption under the pictures, and that really hasn't helped. I will try adding the alt text.

give a tittle to you picture and some descriptions with it,like;
place where you take it ?
what is your message?
etc.
that would give more relative ads.