While the alt text of an image link is important, they are dwarfed by the importance of
description meta-tags, and
It is not clear if your question is SEO related or just good practice, but I think both go hand in hand.
Of course you have decide the look and feel of your site, but I recommend that you do not forget the basics which goes directly to answering your question. So here goes.
You know the SERPs are comprised of a link and content snippet. These come from the
title tag and
description meta-tag respectively under well tune circumstances. As well, the first (and only)
h1 tag should be an extension and alternative to the
title tag and never a direct copy.
In fact, it is wise not to make any element a direct copy of another or too close otherwise. Similar and complimentary yes, copy no.
title tag, make it succinct and compelling and no more 55 characters and not so short that Google makes up a title. This is a click-through opportunity. In your case, it can be the painting title and artist name as a suggestion. You decide what is important. Just remember that your goal is for the
title tag to become the link in the SERPs.
description meta-tag, make it compelling and no more than 150 characters. Make it stand out. This is a click-through opportunity. Between the
title tag and the
description meta-tag, you want to engage your potential user better than anyone.
I always suggest always using an
h1 tag. This can be simple, but make sure it is keyword laden where as the
title tag for CTR, the
h1 tag is not. In your case, it can be the painting title and artist name expanded with some other important keywords such as impressionist, scenic, etc. You decide.
I always suggest having content. It does not have to be much, but the more the merrier. If all you can muster is a paragraph, that is fine. Just be somewhat verbose if that is not your nature. But make sure you have it. Give the search engines something to chew on.
Image alt text should be succinct as well. It should be somewhere between your
description meta-tag and
h1 tag. Keep in mind that the image alt text is indexed and weighted, but not as much as the other elements above.
Here is the rub. If you are looking for image search primarily, then this should do well to support your image. Google at least, and likely Bing too, look for as many clues as possible as to what the image is. The image alt text is not enough. If you are looking for traditional search, then this formula will work too. You will need to track your performance and adjust your various tags use of keywords to attract the right user. But the formula is spot on for both. Remember that text search supports image search. What my point is, make sure that you give the search engines enough of something that they will want to return your page in the SERPs. If a page does well in traditional search, it will also do well in image search. Search engines need something to chew on or they will ignore your site/pages. They also need as many clues as you can give them to know how to return results in image searches and the image alt text is not enough to do that.