Search engines currently do not understand the content of images so its up to you to give them some clues.
The Alt and Title attributes have a very similar effect in regards to SEO, both are important but for different reasons.
The Alt attribute should contain a textual description of the image contents. Originally this was designed for text-based web browsers and people with slow connections, but these days search engines use them too. You will find that if the browser cannot locate the image, it will instead create a rectangle with the Alt text inside.
In some versions of Internet Explorer the contents of the Alt attribute are also show when the user hovers their mouse icon over the image.
The Title attribute can also be used in a similar way to the Alt attribute, but gives you another opportunity to put some keywords to use.
<meta name="keywords" content="Jam,Strawberry Jam,Homemade Strawberry Jam,<your company> Strawberry Jam, Fresh Strawberry Jam, English Jam"
/>
Keep your keywords specific to the content of your page, so for example if you also sell Raspberry Jam then adjust your keywords for that page accordingly.
The description meta tag is commonly used by search engines as the description shown on their listings, its importance is often underestimated as whilst it does not carry as much weight as other tags it should been seen as the first impression somebody gets when reading about your site in the search engine results.
The description should be no more than 25-30 words, try to summarise the contents of the page in one sentence and in doing so make sure the most relevant keywords are included near the beginning of your text.
<meta name="description" content="Quality homemade
strawberry jam from <your company> - made in England using
traditional methods."
/>