Sorry for the length, my problem is very simple, but specific.
I’m building a wordpress site that automatically imports image galleries from a Tumblr account, then styles and displays them. The backend is finished, and all that I need now is have all images in posts be displayed as thumbnail sized links. They are not behaving well with the importer (I’ve tried 6), so I have to edit the HTML display (rather than the images as they are uploaded).
I have decided to do this by applying
class="attachment-thumbnail size-thumbnail" on all images on the site (in HTML). I have tested this and they will open the proper gallery in a lightbox as necessary so long as they belong to those two classes.
I have a two part problem.
From other answers I’ve learned that I should most likely edit the wp_insert_attachment() function in post.php under wp_includes/. I have found the function, but don’t really know where to go from there, as it does not appear to be specific to image attachments. I don’t want to throw any errors by assinging image classes to non-image attachments. How do I add those two classes (attachment-thumbnail and size-thumbnail) to all post images (and only images)?
It seems like the way to handle this would be to allow page attachments to be handled normally, while attachments that are both images and attached to posts should trigger this:
if [attachment is an image AND is on a post, not a page]:
tl; dnr: ^^ that’s all I need to happen, in PHP, in the right file, in WordPress ^^