Feature summary (what you would like to be able to do and where):

I hope users can define classes for specific gallery images.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

I would like to add |class=notpageimage for images in galleries to exclude them from becoming page images. However, I found that you cannot define classes for specific gallery images.

Here is an example:

[[File:Example.png|class=notpageimage|Example]]
<gallery>
File:Example.png|class=notpageimage|Example
File:Example.png|Example|class=notpageimage
</gallery>

In the output, the separate image does have class "notpageimage", but images in the gallery don't. Their captions are "Example" and "class=notpageimage" respectively.

Benefits (why should this be implemented?):

Sometimes it's necessary to define classes for specific gallery images, for example, to exclude them from becoming page images.