depends how duplicated text is. for example part of text from one of my client's page: IM Trading system is forex analysis software that is useful for beginners, providing them credible signals to enter a deal, as well for already successful traders, by confirming their forecasts and improving profitable deal percentage. And next to it if I put screenshot of the program and put alt with: IM Trading system forex analysis software screensot - it will not be duplicated content. Just put some relevant text to relevant images. If you put a lot of 1x1 transparent gifs and try to put all necessary keywords in them than you could expect ban of course. Actually on-site SEO is very very simple. You should follow very simple rules and do not cheat, do not invent bicycle. Use common tags, put relevant alt tags that really are related to the image
See that is a problem,i pulling from same source alt and text description content which make it competly duplicate and since i handle with a lot of pictures i cant make those two different.Also i noticed google pulls description of site from alt tags,now i wonder if i remove alt tags will it ignore regular text.Somehow i have feeling how description text need to be either alt tag or link which leads to somewhere.
i doubt it's impossible to transform this image alts so that it would be different at least a little. make it at least like: image related to: your text your text or your text your text image in some projects in lists i put item same title + word "image" in alt tag and that's it. no ban or penalty. do it smart and no problem