I realize this is question has some age on it, but I thought I would offer a more clear explanation for any future curious Gimp users.
No option to link within Gimp. So... Save the image as a .png or .jpg or .gif. I often create images in GIMP, saving them as a .png file. You can use Open Office (I prefer Open Office vs LibreOffice... Better control and functionality) I will not use LibreOffice. Not professional enough for me.
Open new document in Open Office. Add your text, Add your image. You can drag the image onto the page or can use the "add image" function. Can work with the image functions for Inline |Wrap text. Once the image is added, can then hyperlink to the image. Hyperlink function will be in the toolbar. A small window opens with a section for adding the url. I like to add the full natural url which includes the http(s)://www.....
Save the document. Open office will autosave, but I like to make sure it's saved. Can save as Open Office doc or alternative such as MS Word Doc.
Once saved, then export as a PDF file. Export function is under "File". As an alternative to the pdf function in the program, I use a PDF writer program called PrimoPDF (Google it).
I use the free version, and it allows me to print any doc as a pdf and depending on the use or purpose, can print based on multiple options ranging from screen, ebook, print, prepress and custom options. The different options provide different files sizes. The may be smaller than the PDF file created in Open Office. Additionally, I can control who prints, security, password, etc from within the PrimoPDF options.