The WordPress iOS app tends to favour setting a default post format value depending on the content. What you are seeing is called a Post Format, you can read all about them here. It sounds to me like you’re using a default WordPress theme or a theme that uses post formats.

The default TwentyEleven WordPress theme uses post formats, so you’ll find if you’re using it the offending code will be in the root directory of the theme and be called content-image.php, this file only gets called if a post is assigned to the post format value of image.

I presume you’re using the “Quick Photo” option in the app? This update page for the app shows that using “Quick Photo” will use a post format of image if your theme supports it. Is the issue here that image is being added to blog titles, or you can see the type images showing up in your posts lists but from a front-end perspective the titles are fine?

Updated answer based on response

In your theme function.php file add the following line:

add_theme_support('post-formats', array('aside', 'chat', 'gallery', 'image', 'link', 'quote', 'status', 'video', 'audio'));

Then once you edit a post you’ll notice a post formats box on the right hand side and if it’s post formats that are causing the addition of image to your posts, then you should see the offending post has a post format of image.