Using dynamic variable in each

<th:block th:each="someData, index : ${someData.from.somewhere}">
    <th:block th:each="image : ${images.foo0bar}">
        <img th:src="${image}"/>
    </th:block>
    <hr/>
</th:block>

I want 0 in images.foo0bar to be replaced by index

How do I do something like th:each="image : ${images.foo + index + bar}"

You can use Thymeleaf's preprocessor to execute a getter based on a concatenated string:

__${...}__

For example:

<th:block th:each="someData, iterstat : ${someData}">
    <th:block th:with="imageField=|images.foo${iterstat.index}bar|">
        <th:block th:each="image : ${__${imageField}__}">
            <img th:src="${image}">
        </th:block>
    </th:block>
</th:block>

In the above approach, the th:with="imageField=..." is used to build the string you need:

images.foo0bar  
images.foo1bar  
... and so on...

That imageField variable is then used with the Thymeleaf preprocessing syntax to handle it as a field name in your images object.

UPDATE

My solution above had a mistake, as originally written. Instead of this:

__${imageField}__

It should be this:

${__${imageField}__}

In other words, I forgot to wrap the pre-processor results in a Thymeleaf expression - so that the actual objects in each list (of image URLs) are retrieved.

I corrected this, above.

For backgound, here is the test data I used for the Thymeleaf model:

List<String> someData = Stream.of("abc", "def", "ghi")
        .collect(Collectors.toList());

List<String> a = Stream.of("1", "2", "3")
        .collect(Collectors.toList());
List<String> b = Stream.of("4", "5", "6")
        .collect(Collectors.toList());
List<String> c = Stream.of("7", "8")
        .collect(Collectors.toList());

Images images = new Images();
images.setFoo0bar(a);
images.setFoo1bar(b);
images.setFoo2bar(c);

Map<String, Object> model = new HashMap<>();
model.put("someData", someData);
model.put("images", images);

And my Images class contains these 3 fields:

private List<String> foo0bar;
private List<String> foo1bar;
private List<String> foo2bar;

Just a suggestion...

The Java objects which support this appear to be a bit convoluted, behind the scenes.

You have a collection of someData which you do not directly access, except to iterate through a count of its contents.

You then use this count to build a field name, so you can executed the related getter - and iterate through that collection of image URLs, in a completely different (seemingly unrelated) object.

Just as a suggestion: If you re-arrange your Java data, you could avoid this Thymeleaf complexity.