Any picture on the internet can be put on here. If it's your own (like on Flickr or whatever site) or any other picture. Try to find to right link to the picture: it should end with a picture extension (like .jpg or .png or .gif ...) and put it between
Join an image sharing site,going through the registration etc,then uploading your pics to there,sorting them into a file.then go through the learning process to work out how to link individual pics without sharing your entire collection.Finally link the pic files to here.
In all fairness uploading directly to the thread means ensuring that the image file size meets the forum requirements. If the image was taken on any standard setting of a camera made this century then odds are that the file size is too large.
If this is the case it becomes one hell of a lot more complex to resolve, and is indeed probably why we keep seeing people asking how the feck to do it. Therefore the simplest option is sadly to use a third party image host which automatically resizes (eg, resizes for monitor sizes such as 15" mentioned above) the picture and provides you with pre-set url options including image tags to copy and paste onto the forum.
I say sadly use a third party site as I do think it would be nice to have all the images uploaded to the retrobike servers located in retrobike hall, to add to the fantastic content available through this resource.
But the image size issue associated with direct uploads makes this a pain in the arse to the point where I prefer to use a third party. Opening an image editor, running through various methods of resizing the image, compressing the image then saving as a new copy of the original in order to have something reduced enough to use on the site whilst maintaining the original HQ file before even getting to the upload stage is a lot slower and more in depth than preselecting "image for 15 inch screen" and hitting upload on a whole series of files on the likes of flickr or photobucket. And I know my way around imaging software/Pc's/the interwebnetwork fairly well, any one not quite so familiar is doomed to create threads such as this.