I have seen the mismatched image and text appear in technology blogs where the author has been talking about computer RAM and included on the page is a picture of a sheep. RAM, sheep, get it? It's the sort of thing that happened in the 1980s in some computer magazines I used to know.
There are countless stock image collections on the web, but the best of the bunch must surely be Getty Images. There are millions of images and many of them are unique and high quality. For these reasons they are often used for top web and print publications.
They are expensive though and it can cost hundreds of dollars/pounds for the right to use an image. The web being the lawless place that it is, often uses Getty images without payment. It's just so easy to copy an image from a site and use it elsewhere, such as your own blog or site.
Perhaps this is the reason why a huge number of Getty images are now free to use. Go to the Getty Embed Images page and click the link search images available to embed. You can then search for images.
When you find a suitable image, click it to open a pop-up window and if it has a < > button it can be used in your website or blog. (There are some limitations, but these are mainly to prevent images being used to endorse or advertise products or services.)
Click the < > button and a pop-up window displays some HTML code. Copy this and paste it into your site's code. (Don't use normal wysiwyg editing mode, switch to HTML, plain text or whatever you use for editing). The image may not appear until the page is live on the web because it pulls in the image directly from he Getty Images site.
You will only get low resolution images this way and if you need higher resolution ones you will still have to pay. However, it is a fantastic resource.